In order to study the characteristics of the state-of-art Brake-by-Wire (BBW) systems, the structure and model of the electromechanical brake (EMB) actuator was discussed. Then, in terms of the nonlinear properties of the braking process and the complexity of road conditions, the dynamics of quarter vehicle was presented. Finally, to regulate the slip-ratio of the vehicle under brake while making use of the friction provided by the road, a sliding mode controller (SMC), which was able to control chatter, was designed and computer simulation was studied under Matlab/Simulink. The results have shown the feasibility of the proposed sliding mode controller, and its comparison with PID controller has demonstrated its advantages over PID controller.