Conventional hydraulic steering system has the problems of "low-speed heavy, high-speed flight" and energy-wasting when steering, the main reason is after the system is designed, the power characteristics are fixed. To solve this problem it is necessary to achieve the power characteristics of changing power steering system according to speed of vehicles, in order to offer the power that matches the speed. Using vehicle speed sensor signal to control pilot solenoid unloading valve to regulate the pressure of hydraulic system, can achieve the regulation of power characteristics, this article is based on such idea to design variable hydraulic power steering system for hydraulic power steering system of light trucks.