In order to improve the reliability of the permanent magnet synchronous motor (PMSM) servo system, a dualredundancy PMSM servo system based on multiple parallel branches was given, the basic principles of redundancy design and control driving were proposed. Besides the mathematical models of the dualredundancy PMSM servo system based on multiple parallel branches were built, including magnetic chain equilibrium equation, voltage balance equation, torque equation, mechanical motion equation and the block diagram of current control system as well as stability analysis. According to mathematical model, the simulation of its failure working state was conducted to verify the faulttolerant performance of dualredundancy PMSM servo system based on MATLAB/Simulink.