For the position control of a three-phase separator in certain oil and gas field, the PID parameters need to be adjusted frequently and the control effect is not very good. In order to improve the control accuracy, reduce the impact on downstream process and reduce the work intensity of maintenance personnel,the PID function block of DCS system by Zhejiang University is improved.Different from the original method of integral separation of PID function blocks, the integral function of the PID algorithm is removed when the absolute value of the error between the measured value and the set value becomes smaller.The mathematical model of the control object is established,and the performance of the improved algorithm and the possible negative effects of the algorithm are verified by simulation with MATLAB software.The simulation results show that the improved PID algorithm can better restrain the system oscillation caused by the integral of the PID.For the same control object, the improved algorithm can choose more widely the parameters of the PID, greatly reduce the difficulty of setting the parameters of the PID,and enhance the robustness of the control system,but it may cause the speed of error elimination of the system to become very slow.The improved PID algorithm is applied in the actual DCS control system, and good results are obtained in accordance with the simulation results.