diff --git a/cmd/explaintest/r/explain_indexmerge.result b/cmd/explaintest/r/explain_indexmerge.result
index 83bc89a593e7c..40e0cb4a1159d 100644
--- a/cmd/explaintest/r/explain_indexmerge.result
+++ b/cmd/explaintest/r/explain_indexmerge.result
@@ -6,19 +6,23 @@ create index td on t (d);
 load stats 's/explain_indexmerge_stats_t.json';
 explain format = 'brief' select * from t where a < 50 or b < 50;
 id	estRows	task	access object	operator info
-TableReader	98.00	root		data:Selection
-└─Selection	98.00	cop[tikv]		or(lt(test.t.a, 50), lt(test.t.b, 50))
-  └─TableFullScan	5000000.00	cop[tikv]	table:t	keep order:false
+IndexMerge	98.00	root		
+├─TableRangeScan(Build)	49.00	cop[tikv]	table:t	range:[-inf,50), keep order:false
+├─IndexRangeScan(Build)	49.00	cop[tikv]	table:t, index:tb(b)	range:[-inf,50), keep order:false
+└─TableRowIDScan(Probe)	98.00	cop[tikv]	table:t	keep order:false
 explain format = 'brief' select * from t where (a < 50 or b < 50) and f > 100;
 id	estRows	task	access object	operator info
-TableReader	98.00	root		data:Selection
-└─Selection	98.00	cop[tikv]		gt(test.t.f, 100), or(lt(test.t.a, 50), lt(test.t.b, 50))
-  └─TableFullScan	5000000.00	cop[tikv]	table:t	keep order:false
+IndexMerge	98.00	root		
+├─TableRangeScan(Build)	49.00	cop[tikv]	table:t	range:[-inf,50), keep order:false
+├─IndexRangeScan(Build)	49.00	cop[tikv]	table:t, index:tb(b)	range:[-inf,50), keep order:false
+└─Selection(Probe)	98.00	cop[tikv]		gt(test.t.f, 100)
+  └─TableRowIDScan	98.00	cop[tikv]	table:t	keep order:false
 explain format = 'brief' select * from t where b < 50 or c < 50;
 id	estRows	task	access object	operator info
-TableReader	98.00	root		data:Selection
-└─Selection	98.00	cop[tikv]		or(lt(test.t.b, 50), lt(test.t.c, 50))
-  └─TableFullScan	5000000.00	cop[tikv]	table:t	keep order:false
+IndexMerge	98.00	root		
+├─IndexRangeScan(Build)	49.00	cop[tikv]	table:t, index:tb(b)	range:[-inf,50), keep order:false
+├─IndexRangeScan(Build)	49.00	cop[tikv]	table:t, index:tc(c)	range:[-inf,50), keep order:false
+└─TableRowIDScan(Probe)	98.00	cop[tikv]	table:t	keep order:false
 set session tidb_enable_index_merge = on;
 explain format = 'brief' select * from t where a < 50 or b < 50;
 id	estRows	task	access object	operator info
diff --git a/planner/core/testdata/integration_suite_out.json b/planner/core/testdata/integration_suite_out.json
index 47fb9e613358d..e5a26b74b681c 100644
--- a/planner/core/testdata/integration_suite_out.json
+++ b/planner/core/testdata/integration_suite_out.json
@@ -911,14 +911,16 @@
           "PartitionUnion 59.97 root  ",
           "├─IndexMerge 19.99 root  ",
           "│ ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p0, index:b(b) range:[1,1], keep order:false, stats:pseudo",
-          "│ ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p0, index:c(c) range:[\"8\",\"8\"], keep order:false, stats:pseudo",
+          "│ ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p0, index:c(c) range:[\"8\",\"8\"], keep order:false, stats:pseudo" ,
           "│ └─TableRowIDScan(Probe) 19.99 cop[tikv] table:t, partition:p0 keep order:false, stats:pseudo",
-          "├─TableReader 19.99 root  data:Selection",
-          "│ └─Selection 19.99 cop[tiflash]  or(eq(test.t.b, 1), eq(test.t.c, \"8\"))",
-          "│   └─TableFullScan 10000.00 cop[tiflash] table:t, partition:p1 keep order:false, stats:pseudo",
-          "└─TableReader 19.99 root  data:Selection",
-          "  └─Selection 19.99 cop[tiflash]  or(eq(test.t.b, 1), eq(test.t.c, \"8\"))",
-          "    └─TableFullScan 10000.00 cop[tiflash] table:t, partition:p2 keep order:false, stats:pseudo"
+          "├─IndexMerge 19.99 root  ",
+          "│ ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p1, index:b(b) range:[1,1], keep order:false, stats:pseudo",
+          "│ ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p1, index:c(c) range:[\"8\",\"8\"], keep order:false, stats:pseudo" ,
+          "│ └─TableRowIDScan(Probe) 19.99 cop[tikv] table:t, partition:p1 keep order:false, stats:pseudo",
+          "└─IndexMerge 19.99 root  ",
+          "  ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p2, index:b(b) range:[1,1], keep order:false, stats:pseudo",
+          "  ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p2, index:c(c) range:[\"8\",\"8\"], keep order:false, stats:pseudo", 
+          "  └─TableRowIDScan(Probe) 19.99 cop[tikv] table:t, partition:p2 keep order:false, stats:pseudo"
         ],
         "Warn": null
       },
@@ -934,9 +936,10 @@
           "│ ├─TableRangeScan(Build) 1.00 cop[tikv] table:t, partition:p1 range:[1,1], keep order:false, stats:pseudo",
           "│ ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p1, index:b(b) range:[2,2], keep order:false, stats:pseudo",
           "│ └─TableRowIDScan(Probe) 11.00 cop[tikv] table:t, partition:p1 keep order:false, stats:pseudo",
-          "└─TableReader 11.00 root  data:Selection",
-          "  └─Selection 11.00 cop[tiflash]  or(eq(test.t.a, 1), eq(test.t.b, 2))",
-          "    └─TableFullScan 10000.00 cop[tiflash] table:t, partition:p2 keep order:false, stats:pseudo"
+          "└─IndexMerge 11.00 root  ",
+          "  ├─TableRangeScan(Build) 1.00 cop[tikv] table:t, partition:p2 range:[1,1], keep order:false, stats:pseudo",
+          "  ├─IndexRangeScan(Build) 10.00 cop[tikv] table:t, partition:p2, index:b(b) range:[2,2], keep order:false, stats:pseudo",
+          "  └─TableRowIDScan(Probe) 11.00 cop[tikv] table:t, partition:p2 keep order:false, stats:pseudo"
         ],
         "Warn": null
       },
diff --git a/planner/core/testdata/plan_suite_out.json b/planner/core/testdata/plan_suite_out.json
index 75db6cb736e99..fe29ebe00163c 100644
--- a/planner/core/testdata/plan_suite_out.json
+++ b/planner/core/testdata/plan_suite_out.json
@@ -286,9 +286,9 @@
       },
       {
         "SQL": "select /*+ USE_INDEX_MERGE(t1, c_d_e, f_g) */ * from t where c < 1 or f > 2",
-        "Best": "TableReader(Table(t)->Sel([or(lt(test.t.c, 1), gt(test.t.f, 2))]))",
+        "Best": "IndexMergeReader(PartialPlans->[Index(t.c_d_e)[[-inf,1)], Index(t.f)[(2,+inf]]], TablePlan->Table(t))",
         "HasWarn": true,
-        "Hints": "use_index(@`sel_1` `test`.`t` )"
+        "Hints": "use_index_merge(@`sel_1` `t` `c_d_e`, `f`)"
       },
       {
         "SQL": "select /*+ NO_INDEX_MERGE(), USE_INDEX_MERGE(t, primary, f_g, c_d_e) */ * from t where a < 1 or f > 2",
@@ -304,15 +304,15 @@
       },
       {
         "SQL": "select /*+ USE_INDEX_MERGE(db2.t) */ * from t where c < 1 or f > 2",
-        "Best": "TableReader(Table(t)->Sel([or(lt(test.t.c, 1), gt(test.t.f, 2))]))",
+        "Best": "IndexMergeReader(PartialPlans->[Index(t.c_d_e)[[-inf,1)], Index(t.f)[(2,+inf]]], TablePlan->Table(t))",
         "HasWarn": true,
-        "Hints": "use_index(@`sel_1` `test`.`t` )"
+        "Hints": "use_index_merge(@`sel_1` `t` `c_d_e`, `f`)"
       },
       {
         "SQL": "select /*+ USE_INDEX_MERGE(db2.t, c_d_e, f_g) */ * from t where c < 1 or f > 2",
-        "Best": "TableReader(Table(t)->Sel([or(lt(test.t.c, 1), gt(test.t.f, 2))]))",
+        "Best": "IndexMergeReader(PartialPlans->[Index(t.c_d_e)[[-inf,1)], Index(t.f)[(2,+inf]]], TablePlan->Table(t))",
         "HasWarn": true,
-        "Hints": "use_index(@`sel_1` `test`.`t` )"
+        "Hints": "use_index_merge(@`sel_1` `t` `c_d_e`, `f`)"
       }
     ]
   },
diff --git a/sessionctx/variable/sysvar.go b/sessionctx/variable/sysvar.go
index 9a3e147329b8c..2eee9fb6ac9f5 100644
--- a/sessionctx/variable/sysvar.go
+++ b/sessionctx/variable/sysvar.go
@@ -1075,7 +1075,7 @@ var defaultSysVars = []*SysVar{
 		s.SetEnableCascadesPlanner(TiDBOptOn(val))
 		return nil
 	}},
-	{Scope: ScopeGlobal | ScopeSession, Name: TiDBEnableIndexMerge, Value: Off, Type: TypeBool, SetSession: func(s *SessionVars, val string) error {
+	{Scope: ScopeGlobal | ScopeSession, Name: TiDBEnableIndexMerge, Value: On, Type: TypeBool, SetSession: func(s *SessionVars, val string) error {
 		s.SetEnableIndexMerge(TiDBOptOn(val))
 		return nil
 	}},