The cleaning pump is an essential part of the concrete pump truck. Its necessary power of actual matching is very low (about 3 kW), while the engine power of the concrete pump truck is very large (about 287 kW). Now the cleaning pump hydraulic system of the concrete pump truck, all adopt fixed displacement pump and constant displacement motor system, when the engine running at a high speed and fixed displacement pump system flow is very large, the cleaning pump pump out high pressure washing water, while the engine running at a idle speed and fixed displacement pump system flow is very low, the cleaning pump works abnormally and the water pressure is too low. Aimed at this problem, a sort of design of hydraulic flow matching device for fixed displacement pump and constant displacement motor system was provided. The application of this sort of device was able to let cleaning pump system working normally, and the washing water pumped out at a normal high pressure at the speed of concrete pump truck engine from idle to full under various operating conditions. More over by using AMESim software, the simulation model of flow matching device was established, and simulation analysis for the dynamic characteristics of working of the flow matching device was done. The simulation results show that the dynamic working performance is fully met the requirements of design.