Through the implementation of active rear-wheel steering (ARS), the steering response of the vehicle is significantly improved. In order to enhance the maneuverability of the vehicle, a time-varying parameter-based Linear Quadratic Regulator (LQR) rear wheel steering control method is proposed in this paper. A rear wheel steering dynamic model is established to analyze the load transfer. Steady-state turning tests under different lateral accelerations are conducted to obtain the lateral stiffness at different lateral accelerations. The stiffness values are then used to update the matrices in order to design a variable weighting objective function that balances tracking errors and control inputs. Simulation results demonstrate that the proposed control method effectively enhances the vehicle maneuverability performance. The yaw rate tracking error is controlled within 0.59 deg/s and the sideslip angle is reduced at the same time. Additionally, the rear wheel steering angle exhibits smooth variations, effectively improving the vehicle stability.