Brake-by-wire technology is a development direction of the future automotive brake technology which has aroused extensive concern of domestic and foreign car manufacturers. Since the existing automotive electromechanical brake (EMB) was lack of wear compensation device which was specified in the national standard, GB12676-2014, an innovative EMB with gap automatic adjustment function was designed. The mathematical models of drive motor, motor friction, worm and gear, ball screw and loading were established by MATLAB/Simulink. By building the EMB bench, the braking performance differences between simulation and experiment were tested and analyzed under the signal of step, triangle wave, square wave and sinusoidal wave. The braking performances of EMB with the gap automatic adjustment function or nor were also tested and analyzed. The experimental results showed that the start-current of the EMB system had a "peak" characteristic and the clamping force was sensitive, which could meet the braking requirements. According to the experimental data, the parameter relations were concluded:the clamping force was linearly related to the locked-rotor current, and the characteristics of cubic polynomial were met by the relationship between clamping force and screw displacement. The correctness of the mathematical model was verified by the simulation and experimental results. A theoretical basis for reducing the force sensor and other devices could be provided by the conclusion of parameters relational characteristics. The experimental outcome indicates that the gap automatic adjustment function of the new EMB can guarantee that the brake gap and the response time are consistent at each time, which can further improve the safety of brakes.