Integrating traditional engine and plunger pump, a new type power equipment─Internal Combustion Fluid Pump(ICFP) was developed, through which thermal energy can be turned into hydraulic pressure directly. As a main factor affecting ICFP’s performances, efficiency is the basis to design its structure. For three-cylinder axial ICFP, it’s dynamics model was setup, and its efficiency character was studied. The simulating results show that ICFP’s effective thermal efficiency is 37.44% at calibration condition, which is higher than engine-pump system by 23.06%. For the three-cylinder ICFP, the effective thermal efficiency experiments are done. Errors are within 5%, and it proved that the simulation results are correct.