The speed ratio of EM- CVT can be adjusted by controlling the motor angle and the power source of speed ratio change is provided by a single motor. The control strategy based on Fuzzy- PID is proposed to improve the control precision of speed ratio control system and the fuzzy- PID is optimized by PSO algorithm. The Fuzzy PID speed ratio controller model is set up,whose parameter factors are optimized by the PSO algorithm to realize the optimization of the speed ratio control system. The simulation is carried out and the results show that the Fuzzy- PID controller optimized by PSO algorithm can improve the control precision of system and the performance of the speed ratio tracking performance.