In view of the flaw exhibited by the current loop in the conventional vector control system when using PI regulator without quadrature-direct axis current coupling, with d-q axis feedback current and feedback speed the input voltage feed forward decoupling unit, the output of the d-q axis current regulator serves as the compensation voltage, thus forming a compound control system with the voltage feed forward decoupling unit combined together. The vector control system of permanent magnet synchronous motor and the voltage feed forward decoupling model are set up under the MATLAB/SIMULINK simulation software, followed by a simulation analysis of the operating condition with load disturbance under three operating modes of metro traction, coasting and braking. The simulation results show that, compared with that of the traditional PI controller, the system of the PI controller based on voltage feed-forward decoupling is relatively superior in that it exhibits a better dynamic performance.