After obtaining the optimal trajectory through the lane change decision and the trajectory planning, the last key technique for the automatic lane change assist system is to carry out the precise and rapid steering execution according to the front wheel angle demand. Therefore, a brushless DC motor model, a steering system model and a whole vehicle model are first established in this paper. Electromagnetic characteristics of the motor, the moment of the inertia and viscous friction etc. are considered in the models. Then, the steering angle tracking control algorithm of the steering motor is designed according to the tracking demand. The control torque of the steering motor is obtained by the steering angle demand, after that, the control current is calculated considering of electromagnetic characteristics of the motor. Debugging and optimization of the control algorithm are done through simulation. Also, the optimum control is studied by comparing different steering angle tracking control algorithms. In addition, the influence of the steering wheel elasticity on lane change stability under different vehicle speeds and front wheel angles is studied in the case of lane change assist. An HIL experiment bench including of steering gear and steering resistance simulation device is also built up. The influence of the error of the mechanical steering linkage on the steering angle tracking accuracy is studied by measuring motor steering angle and rack displacement. Simulation and test results can provide reference for precise steering angle control of the automatic lane change assist system by considering of different parts of the steering system, steering motor-steering linkage-steering wheel.