In order to improve the lateral control performance of unmanned vehicle, a control method based on optimal steering curvature is proposed. The analytical form of the optimal turning curvature is solved by using the vehicle kinematic constraints, and the local stability of the closed-loop system with zero input near the equilibrium point is proved by using the linearization method, and the relationship between the vehicle speed and the preview distance, which guarantees the local stability of the closed-loop system, is quantitatively analyzed by numerical methods; The concept of the optimal preview distance under a certain speed is proposed, and the relationship between the optimal preview distance and the speed is solved by numerical method. The results of simulation and real vehicle experiment show that the unmanned vehicle can still run stably under non-zero input.