Intenal combustion pump(ICP) is a new type power device turning the thermal energy from fuel combustion into fluid pressure energy.Three cylinders prototype has just been developed.The study on the influence of valve’s characteristic on ICP’s total performance will found the base for its optimum design.Based on the theoretical and testing fruits of single cylinder prototype, the performance of the valves and complete appliance of the latest is simulated.When the natural frequency of valves is approximately to the round number times of the working frequency, volumetric efficiency is seriously low.The nominal rotational speed of the prototype is nearly to the speed where the volumetric efficiency is lowest, which is harmful to the normal work of ICP, so further structure optimization of valves should be carried out.The change of volumetric efficiency has great influence on the fuel consumption rate, output flow, effective thermal efficiency, effective power, and so on, but little on output pressure. Intenal combustion pump (ICP) is a new type power device turning the thermal energy from fuel combustion into fluid pressure energy. Three cylinders prototype has just been developed. The study on the influence of valve’s characteristic on ICP’s total performance will found the base for its optimum design. based on the theoretical and testing fruits of single cylinder prototype, the performance of the valves and complete appliance of the latest is simulated. Where the natural frequency of valves is approximately to the round number times of the working frequency, volumetric efficiency is seriously low.The nominal rotational speed of the prototype is nearly to the speed where the volumetric efficiency is lowest, which is harmful to the normal work of ICP, so further structure optimization of valves should be carried out. change of volumetric efficiency has great influence on the fuel consumption rate, output flow, effective thermal efficiency, effective power, and so on, but little on outp ut pressure.