In the view of the problem that the current performance evaluation method of MPC control loop cannot accurately locate the source causing performance degradation. A performance diagnosis method for control loop is proposed based on weighted L2-Hausdorff subspace distance. The method characterizes the loop performance features under different poor operating conditions by using deteriorating performance subspace

and monitors the control loop performance in real time through the model prediction residual based closed-loop potential index. When the performance degradation is detected

weighted L2-Hausdorff subspace distance is constructed to measure the similarity between the current loop performance pattern and the known ones

and the source causing performance degradation is then positioned by distance clustering. Finally

the simulation experiment on the continuous stirred tank heater(CSTH) validates the effectiveness and reliability of the proposed method.