diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionStates.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionStates.java
index 8d22c0e065f..356b0866976 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionStates.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionStates.java
@@ -76,10 +76,17 @@ public class RegionStates {
    * RegionName -- i.e. RegionInfo.getRegionName() -- as bytes to {@link RegionStateNode}
    */
   private final ConcurrentSkipListMap<byte[], RegionStateNode> regionsMap =
-      new ConcurrentSkipListMap<byte[], RegionStateNode>(Bytes.BYTES_COMPARATOR);
+      new ConcurrentSkipListMap<>(Bytes.BYTES_COMPARATOR);
+
+  /**
+   * this map is a hack to lookup of region in master by encoded region name is O(n).
+   * must put and remove with regionsMap.
+   */
+  private final ConcurrentSkipListMap<String, RegionStateNode> encodedRegionsMap =
+    new ConcurrentSkipListMap<>();
 
   private final ConcurrentSkipListMap<RegionInfo, RegionStateNode> regionInTransition =
-    new ConcurrentSkipListMap<RegionInfo, RegionStateNode>(RegionInfo.COMPARATOR);
+    new ConcurrentSkipListMap<>(RegionInfo.COMPARATOR);
 
   /**
    * Regions marked as offline on a read of hbase:meta. Unused or at least, once
@@ -101,6 +108,7 @@ public class RegionStates {
    */
   public void clear() {
     regionsMap.clear();
+    encodedRegionsMap.clear();
     regionInTransition.clear();
     regionOffline.clear();
     serverMap.clear();
@@ -117,8 +125,11 @@ public class RegionStates {
   // ==========================================================================
   @VisibleForTesting
   RegionStateNode createRegionStateNode(RegionInfo regionInfo) {
-    return regionsMap.computeIfAbsent(regionInfo.getRegionName(),
-      key -> new RegionStateNode(regionInfo, regionInTransition));
+    return regionsMap.computeIfAbsent(regionInfo.getRegionName(), key -> {
+      final RegionStateNode node = new RegionStateNode(regionInfo, regionInTransition);
+      encodedRegionsMap.putIfAbsent(regionInfo.getEncodedName(), node);
+      return node;
+    });
   }
 
   public RegionStateNode getOrCreateRegionStateNode(RegionInfo regionInfo) {
@@ -136,6 +147,7 @@ public class RegionStates {
 
   public void deleteRegion(final RegionInfo regionInfo) {
     regionsMap.remove(regionInfo.getRegionName());
+    encodedRegionsMap.remove(regionInfo.getEncodedName());
     // See HBASE-20860
     // After master restarts, merged regions' RIT state may not be cleaned,
     // making sure they are cleaned here
@@ -203,13 +215,11 @@ public class RegionStates {
   }
 
   public RegionState getRegionState(final String encodedRegionName) {
-    // TODO: Need a map <encodedName, ...> but it is just dispatch merge...
-    for (RegionStateNode node: regionsMap.values()) {
-      if (node.getRegionInfo().getEncodedName().equals(encodedRegionName)) {
-        return node.toRegionState();
-      }
+    final RegionStateNode node = encodedRegionsMap.get(encodedRegionName);
+    if (node == null) {
+      return null;
     }
-    return null;
+    return node.toRegionState();
   }
 
   // ============================================================================================