The battery electric vehicles and the intelligent vehicles put forward new requirements (such as independent of vacuum brake booster, active brake or automatic emergency braking) for the braking system, which is a key link of vehicle active safety and automatic driving. The traditional vacuum brake booster is no longer able to meet these requirements. In this paper, a novel integrated electric assist actuator of brake system aimed at boosting pedal force of driver, independent of vacuum source, and supplying autonomous emergency braking (AEB) or active braking, and even achieving regenerative braking is proposed to improve the vehicle brake performance. Such an electro-mechanical brake booster system consisted of PMSM, double reduction transmission by gears and ball screw, servo body, and reaction disk. The precise control of pressure-force is the key to the reliability of the brake. Owning to the high cost of force sensors and inconvenient installation, we translate the control problem of force to position tracking. However，the strong nonlinearity and the load-dependent friction makes the position control of the electro-mechanical brake booster system becomes more challenging. Consequently, a modified PID control architecture with techniques of cascaded three-closed PID framework, friction compensation, and gain scheduling is presented to address the plant nonlinearity based on the established friction model. It is necessary to solve the friction problems existing in the system in such a electromechanical system. Therefore, a Karnopp friction model is adopted and the parameters are identified by the method of multiple linear regression in this paper. Finally, bench tests covering multiple kinds of brake conditions are designed and implemented to verify the performance of controller based on RCP environment. Test results show that both the position tracking performance and response time of electro-mechanical brake booster system perform well.