| A precise control method of clamping force is proposed for train electro-mechanical brake system (EMB). Firstly, the open-loop control characteristics of EMB were studied. Due to the influence of motor-loss , machining and assembly accuracy of mechanical transmission device, internal resistance, there is an error in the force transmission, resulting in poor response on EMB open-loop. Based on the PID control, the closed-loop response characteristics of the system were studied, and the clamping force optimized algorithm was designed by adding buffer process and tracking-differential. Finally, the control accuracy and tracking effect of the clamping force optimized algorithm were verified by hardware-in-loop experiments, meanwhile, the frequency characteristics of the EMB clamping force and the brake cylinder pressure of an electro-pneumatic braking system were contrastive analyzed.