A new method is proposed to optimize the hydraulic torque converter of CVT(continously variable transmission) cars by matching the whole vehicle，i.e.，regarding engine，hydraulic torque converter and transmission system as a system and taking the whole vehicle’s dynamic property and economical efficiency as the target to optimize and improve the parameters of hydraulic torque converter. The designing variable is the circulatory diameter of hydraulic torque converter. Choosing 0~100 km/h accelerate time of full throttle and GB18352.3—2005 cycle fuel consumption as the evaluation indicators of vehicle matching. The best circulatory diameter is obtained by optimizing. The simulation results indicate that optimized accelerating time and fuel consumption reduce，which means this method is helpful for the matching of hydraulic torque converter.