Continuously variable transmission (CVT) is the ideal transmission for automobile, it is also one of the most important research items of researchers and automobile companies all over the world. By studying the force relationship of metal V-belt type continuously variable transmission, an optimum pitch radius is derived to maximize torque capacity, also a design procedure for optimum pitch radius is listed. The design procedure is applied for the true application, the calculation result shows that the torque capacity of belt transmission can be improved by optimization of the pitch radius. The research results provide the theory analysis method and design base for CVT vehicle.