Hydraulic components are widely used in mechanical industry. To comply with the requirements of modern products for high quality and performance, hydraulic components are required to improve their own efficiency and controlling capability. The hydraulic pump, as a main element for energy conversion, exerts tremendous influence on the overall output efficiency of a product. The first is the energy loss analysis of a hydraulic pump, which is aimed to enable the pump to achieve a higher efficiency. Theoretical calculations may deviate to some extent from the experimental data as the equation of fluid motion is calculated based upon the ideal fluid; moreover, the leakage at the tooth meshing though at little amount, the friction loss between the shaft and its bearings, and the friction loss due to the meshing of gears were not considered during modeling. To determine the optimum clearance, it is necessary to take into account the workmanship factors, thermal expansion and contraction, frictional resistance, working conditions and any other factors as a whole. This was followed by obtaining the optimum clearance at the minimal power loss from the energy efficient perspective. These above-mentioned conclusions have some instructional significance over the design of the hydraulic pump.