diff --git a/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/degrade/circuitbreaker/ResponseTimeCircuitBreaker.java b/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/degrade/circuitbreaker/ResponseTimeCircuitBreaker.java
index 51f81316..2ab98d4d 100644
--- a/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/degrade/circuitbreaker/ResponseTimeCircuitBreaker.java
+++ b/sentinel-core/src/main/java/com/alibaba/csp/sentinel/slots/block/degrade/circuitbreaker/ResponseTimeCircuitBreaker.java
@@ -19,7 +19,6 @@ import java.util.List;
 
 import com.alibaba.csp.sentinel.Entry;
 import com.alibaba.csp.sentinel.context.Context;
-import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
 import com.alibaba.csp.sentinel.slots.block.RuleConstant;
 import com.alibaba.csp.sentinel.slots.block.degrade.DegradeRule;
 import com.alibaba.csp.sentinel.slots.statistic.base.LeapArray;
@@ -34,6 +33,8 @@ import com.alibaba.csp.sentinel.util.TimeUtil;
  */
 public class ResponseTimeCircuitBreaker extends AbstractCircuitBreaker {
 
+    private static final double SLOW_REQUEST_RATIO_MAX_VALUE = 1.0d;
+
     private final long maxAllowedRt;
     private final double maxSlowRequestRatio;
     private final int minRequestAmount;
@@ -110,6 +111,10 @@ public class ResponseTimeCircuitBreaker extends AbstractCircuitBreaker {
         if (currentRatio > maxSlowRequestRatio) {
             transformToOpen(currentRatio);
         }
+        if (Double.compare(currentRatio, maxSlowRequestRatio) == 0 &&
+                Double.compare(maxSlowRequestRatio, SLOW_REQUEST_RATIO_MAX_VALUE) == 0) {
+            transformToOpen(currentRatio);
+        }
     }
 
     static class SlowRequestCounter {
diff --git a/sentinel-core/src/test/java/com/alibaba/csp/sentinel/slots/block/degrade/circuitbreaker/ResponseTimeCircuitBreakerTest.java b/sentinel-core/src/test/java/com/alibaba/csp/sentinel/slots/block/degrade/circuitbreaker/ResponseTimeCircuitBreakerTest.java
new file mode 100644
index 00000000..66dd4691
--- /dev/null
+++ b/sentinel-core/src/test/java/com/alibaba/csp/sentinel/slots/block/degrade/circuitbreaker/ResponseTimeCircuitBreakerTest.java
@@ -0,0 +1,58 @@
+package com.alibaba.csp.sentinel.slots.block.degrade.circuitbreaker;
+
+import com.alibaba.csp.sentinel.slots.block.RuleConstant;
+import com.alibaba.csp.sentinel.slots.block.degrade.DegradeRule;
+import com.alibaba.csp.sentinel.slots.block.degrade.DegradeRuleManager;
+import com.alibaba.csp.sentinel.test.AbstractTimeBasedTest;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * @author xierz
+ * @date 2020/10/4
+ */
+public class ResponseTimeCircuitBreakerTest extends AbstractTimeBasedTest {
+    @Before
+    public void setUp() {
+        DegradeRuleManager.loadRules(new ArrayList<DegradeRule>());
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        DegradeRuleManager.loadRules(new ArrayList<DegradeRule>());
+    }
+
+    @Test
+    public void testMaxSlowRatioThreshold() {
+        String resource = "testMaxSlowRatioThreshold";
+        DegradeRule rule = new DegradeRule("resource")
+                .setCount(10)
+                .setGrade(RuleConstant.DEGRADE_GRADE_RT)
+                .setMinRequestAmount(3)
+                .setSlowRatioThreshold(1)
+                .setStatIntervalMs(5000)
+                .setTimeWindow(5);
+        rule.setResource(resource);
+        DegradeRuleManager.loadRules(Collections.singletonList(rule));
+
+        assertTrue(entryAndSleepFor(resource, 20));
+        assertTrue(entryAndSleepFor(resource, 20));
+        assertTrue(entryAndSleepFor(resource, 20));
+
+        // should be blocked, cause 3/3 requests' rt is bigger than max rt.
+        assertFalse(entryAndSleepFor(resource,20));
+        sleep(1000);
+        assertFalse(entryAndSleepFor(resource,20));
+        sleep(4000);
+
+        assertTrue(entryAndSleepFor(resource, 20));
+    }
+
+}