Driven by a hydraulic open loop system, which consisted of engine-CVT-fixed displacement pump and fixed displacement wheel-motors, a 4WD frontaxle articulated vehicle is needed to solve the problem when it is walking in negative loads situation. Currently, most of the hydraulic traveling machinery with open-loop system uses the counterbalance valve to control the negative loads. However, traditional counterbalance valves still have the problems of high cost, difficult maintenance and high power consumption. To solve these problems, a vehicle simulation model was built and tested. The control system included an electro-proportional relief valve, a pressure sensor and electronic control system with programmable processor. The electroproportional relief valve was mounted on the outlet port of the hydraulic system. The pressure sensor was installed on the inlet port of the traveling motors. By reading the signal of the pressure sensor, and adjusting the cracking pressure of the electro-proportional relief valve to realize the hydraulic motors meter-out flow control. The results showed that this system can correctly judge the driver’s intension, improve energy efficiency by reducing the cracking pressure when the vehicle working in positive load. When the vehicle working in negative load, the system would choose the suitable cracking pressure to meet the driver’s expectations and keep the hydraulic motors from overrunning.