Flush valve is the basic component of closed hydraulic system, which combines filling valve with closed pump to realize the thermal balance function.The ratio of flushing overflow Qc to output flow Qp of the fuel pump is called flow distribution ratio k. Due to the influence of engine speed，the pressure on the back of the washing valve, the flow distribution ratio was changed greatly, which could not maintain a constant value or a small change area, affecting the cooling effect of the closed system, and easy to burn the pump. A new type of valve flow self-compensation technique was used, which could avoid the shortage of existing washing valve which was easy to be affected by backpressure and engine speed. After AMESim simulation analysis and benchmark test verification, the newly designed washing valve can avoid the shortcomings of the old washing valve, furthermore, it has new characteristic of a large-scale adjustable flow distribution ratio, so it is very suitable to complex engineering machinery applications.