This article includes the principle of frequency control of motor speed and the Universal Serial (short for USS below) interface protocol. And design of the intelligent braking system based on USS interface protocol will be introduced from the principle of intelligent braking system based on frequency control of motor speed, composition of hardware, software designing and the realization of communication between PLC and frequency converter using USS interface protocol. This system has realized the intelligent adjustment of brake torque and improved the performance of traditional brake. Consequently it will be good for reducing the vibration impulse during the process of braking and enhancing braking stability. So the working life of brakes will be expanded.