Due to the height limitation of coal mine roadway, the explosion-proof diesel engine concrete mixing truck is driven by closed hydraulic system. In the actual use process, there are problems of sudden deceleration when the accelerator pedal is loosened and abnormal noise when braking. In view of this situation, this paper analyzes the fault analysis and hydraulic principle of the vehicle, and finds that the problem stems from the excessive speed reduction, the irregular operation of the driver and the loosening of the fixed bolts caused by the melting of the internal thread glue of the axle. In order to solve these problems, solutions such as optimizing the damping hole of the variable pump, increasing the integrated valve group with one-way pressure relief and increasing the speed stabilization function are proposed. Through field tests, these schemes effectively improve the downhill driving performance of vehicles, and improve driving comfort and safety.