Electric power steering system is developed by applying the electric machine as a steering assistant power based on mechanical steering system. It can change the steering force transmission characteristics easily, reduce the driver load, and improve the vehicle maneuverability and handling performance. But as the users increasing demand in handling and stability of vehicle, we need take adaptive control stability in steering system, especially when yaw velocity or lateral acceleration exceeding the threshold valve, taking the adaptive control stability.This paper presents a new concept to prevent over-steering in the turning. Installed yaw velocity sensor in the vehicle, detecting the yaw velocity signal and delivering to the CPU, who should calculates the value of steady turning to control the power steering motor, and to ensure under-steering in the turning.We build a simulation model in the AMEsim software, gaining the yaw velocity value at the neutral steering. In order to improve the stable running in the turning, the yaw acceleration sensor was installed in the vehicle. When the yaw acceleration rate exceeds a critical value, the motor will be controlled to prevent over-steering.