Under the research background of the pneumatic control system of new mooring mechanism，taking its single pneumatic branch as an example，the dynamic mathematical model of proportional pressure valve control cy-linder was established and verified by experiments． Given the control mode of independent load port，namely，one cavity is position closed loop and the other is constant pressure control mode，the high frequency and low amplitude chatter signal was superimposed on the control signal of the constant pressure chamber to compensate the friction force． The simulated and experimental results show that chatter compensation improves the positioning accuracy of the system from 1. 1mm to 0. 5mm．