Abstract: In this article, the bigger tire cornering stiffness and the smaller tire cornering stiffness were connected with the weighted functions to synthesize a nonlinear equation of state of vehicle. The optimal theory of linear quadratic regulator was used to design a synthetic controller to control the four wheels steering car, considering the nonlinear character of tire cornering stiffness. The software of Matlab/Simulink and Carsim were used for a co-simulation to test the performance of the controller. The results of the simulation show that, when the car is carrying out a double lane change on the low adhesion coefficient road, the four wheels steering car controlled by LQR method can give a better handling performance than front wheels steering car, and the four wheels steering car controlled by LQR synthetic controller which considers the non-liner tire stiffness can give good handling performance than LQR controller which considers only the liner tire stiffness.