diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/cost/CostModelV1.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/cost/CostModelV1.java
index c6bb6e6fdff2d91..8b2a09ca07b8043 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/cost/CostModelV1.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/cost/CostModelV1.java
@@ -67,6 +67,7 @@ class CostModelV1 extends PlanVisitor<Cost, PlanContext> {
     // the penalty factor is no more than BROADCAST_JOIN_SKEW_PENALTY_LIMIT
     static final double BROADCAST_JOIN_SKEW_RATIO = 30.0;
     static final double BROADCAST_JOIN_SKEW_PENALTY_LIMIT = 2.0;
+    static final double RANDOM_SHUFFLE_TO_HASH_SHUFFLE_FACTOR = 0.1;
     private final int beNumber;
 
     public CostModelV1() {
@@ -226,10 +227,11 @@ public Cost visitPhysicalDistribute(
         }
 
         // any
+        // cost of randome shuffle is lower than hash shuffle.
         return CostV1.of(
-                intputRowCount,
                 0,
-                0);
+                0,
+                intputRowCount * childStatistics.dataSizeFactor() * RANDOM_SHUFFLE_TO_HASH_SHUFFLE_FACTOR / beNumber);
     }
 
     @Override
diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/properties/ChildrenPropertiesRegulator.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/properties/ChildrenPropertiesRegulator.java
index 93f6e947894c832..4a2ecdd098b11d9 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/properties/ChildrenPropertiesRegulator.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/properties/ChildrenPropertiesRegulator.java
@@ -41,6 +41,7 @@
 import org.apache.doris.nereids.trees.plans.physical.PhysicalPartitionTopN;
 import org.apache.doris.nereids.trees.plans.physical.PhysicalProject;
 import org.apache.doris.nereids.trees.plans.physical.PhysicalSetOperation;
+import org.apache.doris.nereids.trees.plans.physical.PhysicalUnion;
 import org.apache.doris.nereids.trees.plans.visitor.PlanVisitor;
 import org.apache.doris.nereids.util.JoinUtils;
 
@@ -115,6 +116,16 @@ public Boolean visitPhysicalHashAggregate(PhysicalHashAggregate<? extends Plan>
                 && children.get(0).getPlan() instanceof PhysicalDistribute) {
             return false;
         }
+
+        // agg(group by x)-union all(A, B)
+        // no matter x.ndv is high or not, it is not worthwhile to shuffle A and B by x
+        // and hence we forbid one phase agg
+        if (agg.getAggMode() == AggMode.INPUT_TO_RESULT
+                && requiredProperties.get(0).getDistributionSpec() instanceof DistributionSpecHash
+                && children.get(0).getPlan() instanceof PhysicalUnion
+                && !((PhysicalUnion) children.get(0).getPlan()).isDistinct()) {
+            return false;
+        }
         // forbid multi distinct opt that bad than multi-stage version when multi-stage can be executed in one fragment
         if (agg.getAggMode() == AggMode.INPUT_TO_BUFFER || agg.getAggMode() == AggMode.INPUT_TO_RESULT) {
             List<MultiDistinction> multiDistinctions = agg.getOutputExpressions().stream()
diff --git a/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/physical/PhysicalSetOperation.java b/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/physical/PhysicalSetOperation.java
index 83f15e3f6688d97..ec9537e7cb981a0 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/physical/PhysicalSetOperation.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/nereids/trees/plans/physical/PhysicalSetOperation.java
@@ -194,4 +194,8 @@ public List<Slot> computeOutput() {
                 .map(NamedExpression::toSlot)
                 .collect(ImmutableList.toImmutableList());
     }
+
+    public boolean isDistinct() {
+        return qualifier == Qualifier.DISTINCT;
+    }
 }
diff --git a/fe/fe-core/src/main/java/org/apache/doris/statistics/ColumnStatistic.java b/fe/fe-core/src/main/java/org/apache/doris/statistics/ColumnStatistic.java
index c6b019f669b65d3..7fb81065c206e1a 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/statistics/ColumnStatistic.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/statistics/ColumnStatistic.java
@@ -38,7 +38,7 @@
 public class ColumnStatistic {
 
     public static final double STATS_ERROR = 0.1D;
-
+    public static final double ALMOST_UNIQUE_FACTOR = 0.9;
     public static final StatsType NDV = StatsType.NDV;
     public static final StatsType AVG_SIZE = StatsType.AVG_SIZE;
     public static final StatsType MAX_SIZE = StatsType.MAX_SIZE;
@@ -202,7 +202,7 @@ public static ColumnStatistic fromResultRow(ResultRow row) {
     }
 
     public static boolean isAlmostUnique(double ndv, double rowCount) {
-        return rowCount * 0.9 < ndv && ndv < rowCount * 1.1;
+        return rowCount * ALMOST_UNIQUE_FACTOR < ndv;
     }
 
     public ColumnStatistic updateByLimit(long limit, double rowCount) {