Abstract: The letdown temperature adjustment and control circuit in the Chemical and Volume control system RCV takes on serious time-delay and feeble repellence characteristics when the temperature acutely fluctuates or the outside disturbs both in the Daya Bay nuclear power station and Ling’ao nuclear power station,which cause lies in the value and the inherent pure time-delay characteristics of the heat exchanger in this circuit,as well as the controller used in the circuit is a simple PI controller.By comparison,a more advanced technique,combining the Smith predictive control,adaptive fuzzy control and PID control,is put forward based on theoretical derivation and simulation experimental verification.This technique gives the control system a fine dynamic stability and robustness,to overcome the disadvantage of the original circuit.