The automatic steering system for unmanned vehicle was developed. The magnet and MR (Magnetoresistive) sensors are used for the tue detecting system. The lateral distance between sensor and the center line of the road is determined by the linearization of the distance according to the output. The PD control theory is used for the design of the controller to compare with $H_infty$ control theory. The $H_infty$ control theory is used for the design of the controller to reduce the disturbance. The performance of the PD controller and $H_infty$ controller is compared in simulations and tests. The PD controller is easy to tune in the test site. The $H_infty$ controller is robust far the disturbances in the test results.