Aimed at the shortcoming of the characteristic of unalterable power of commercial vehicles commonly used hydraulic power steering system (HPS), a bypass flow control type of electrical controlled hydraulic power steering (ECHPS) system was introduced. The power control strategy of the steering system was designed, the structure principle and mathematical model of its core component of electrohydraulic proportional valve was studied, and a robust adaptive dynamic surface controller was designed by dynamic surface control method. The theory proves that the designed controller not only can guarantee the closedloop semiglobally asymptotically stable ,and output asymptotic tracking expected trajectory, but also the controller has strong robustness for the uncertain parameters and external disturbances. The simulation results indicate that the designed adaptive dynamic surface controller has not only fast response, good tracking performance and high control accuracy, but also can achieve the requirements of lowspeed light and highspeed good road sense when the vehicle steering.