diff --git a/src/src/main/java/com/my/graphiteDigesterBg/task/TaskLiquidAdd.java b/src/src/main/java/com/my/graphiteDigesterBg/task/TaskLiquidAdd.java
index 0f0e306..01f90f0 100644
--- a/src/src/main/java/com/my/graphiteDigesterBg/task/TaskLiquidAdd.java
+++ b/src/src/main/java/com/my/graphiteDigesterBg/task/TaskLiquidAdd.java
@@ -5,7 +5,8 @@ import com.my.graphiteDigesterBg.model.MdbOperationLog;
 import com.my.graphiteDigesterBg.move.MoveLiquidAdd;
 import com.my.graphiteDigesterBg.move.MoveMoveTubeRackFromHeatPlateToLiquidPlate;
 import com.my.graphiteDigesterBg.move.MoveMoveTubeRackFromLiquidPlateToHeatPlate;
-
+import com.my.graphiteDigesterBg.resource.ResHeatingTubeRackSlotManager;
+import java.util.Objects;
 @Task(name="LiquidAdd")
 public class TaskLiquidAdd extends DiTaskBase {
     // slot index
@@ -20,12 +21,18 @@ public class TaskLiquidAdd extends DiTaskBase {
     @Override
     protected void execute() {
         this.setStatus(TaskStatus.RUNNING);
+        var slotMan = this.getResourceManager(ResHeatingTubeRackSlotManager.class);
+        var slot = slotMan.getSlotAtLiquidPlate();
 
-        // move tube rack from heat plate to liquid plate
-        var moveTubeRackFromHeatPlateToLiquidPlate = new MoveMoveTubeRackFromHeatPlateToLiquidPlate();
-        moveTubeRackFromHeatPlateToLiquidPlate.setDevice(this.getDevice());
-        moveTubeRackFromHeatPlateToLiquidPlate.slotIndex = this.slotIndex;
-        moveTubeRackFromHeatPlateToLiquidPlate.run();
+        if ( slot == null ) {
+            // move tube rack from heat plate to liquid plate
+            var moveTubeRackFromHeatPlateToLiquidPlate = new MoveMoveTubeRackFromHeatPlateToLiquidPlate();
+            moveTubeRackFromHeatPlateToLiquidPlate.setDevice(this.getDevice());
+            moveTubeRackFromHeatPlateToLiquidPlate.slotIndex = this.slotIndex;
+            moveTubeRackFromHeatPlateToLiquidPlate.run();
+        } else if (!Objects.equals(slot.index, this.slotIndex)) {
+            throw new RuntimeException("加液位置已存在试管架， 无法执行加液操作");
+        }
 
         MdbOperationLog.log(this.getUser(), "试管架%d : 样本加液 类型=%s, 加液量=%d", this.slotIndex, this.liquidType, this.liquidVolume);