According to the problem that the intermediate link analysis is insufficient and the accuracy of the parameter setting algorithm is low, a method of modular modeling of multiinertia servo feed system is proposed. The servo feed system of Computer Numerical Control（CNC）machine tool is transformed into a multi inertia system, which is divided into three parts, the motor, the screw and the worktable. Based on PID three closedloop control system, using Matlab software to simulate the vector control system of Permanent Magnet Synchronous Motor（PMSM）and mechanical transmission system model, and then adjusting the parameters. The simulation results show that the modular modeling method can be used to analyze the problems accurately in the multiinertia servo system, and it has a more effective analysis on the middle link of the system. The accuracy of the simulation model and parameter setting algorithm is improved, and the simulation results are good.