Aiming at the limitations of general ratio controller for Continuously Variable Transmission (CVT), an improved PID control algorithm, which has the engineering value, is presented based on the CVT ratio control strategy, an improved PID controller is designed in the Matlab environment. Moreover, considering that the single simulation software is unable to precisely express model parameters, the vehicle model is developed in Cruise, and co-simulation with Simulink model in term of API is conducted. The simulation results show that the designed controller and joint simulation are feasible, the improved speed ratio controller could well follow the target speed ratio and has the good dynamic response and high control accuracy in a steady state, the results of simulation are well consist with the actual status of the prototype cat, the correctness of the theoretical analysis is verified, and also reflected the CVT's technological superiority in terms of vehicle fuel economy and power.