Due to the elimination of the mechanical connection, the steer-by-wire steering system can freely design the angular transmission ratio between the hand steering wheel and the road steering wheel. In this paper, the variable steering ratio control strategies under normal driving conditions and unconventional driving conditions were proposed. The variable steering ratio control of normal driving conditions is based on the ideal yaw rate gain, taking into account the low-speed steering lightness and high-speed steering stability, and the steering ratio varies with the vehicle speed and the hand steering wheel angle, which ensures the vehicle steering sensitivity at low speed and the steering stability at high speed. The variable steering ratio control of the unconventional driving conditions is based on yaw rate dynamic feedback control, and the steering ratio varies with the vehicle movement status. Here we use active steering control which is based on active disturbance rejection control to achieve yaw rate dynamic feedback control, which can improve vehicle stability and has strong robust. In order to verify the effectiveness of the proposed variable ratio control strategy, using CarSim and Simulink to simulate the typical driving conditions, the simulation results show that the variable steering ratio control under normal driving conditions can effectively improve the steering sensitivity at low speed and the steering stability at high speed, so that the vehicle has good handling stability under all vehicle speeds, and the variable steering ratio control under unconventional driving conditions can effectively improve the transient response of the vehicle and improve the vehicle's steering stability and active safety.