This work presents a systematic analysis of the tribological properties of the lubricant and the thermal exchange effect on the deformation of the solid-fluid structure between the piston and cylinder block in an axial piston pump. A thermo-elastohydrodynamic model is established and used to study the pump. Fluid film properties, friction forces and leakage of the solid-fluid structure are calculated and analysed under normal operating conditions of the axial piston pump s. The friction and leakage losses representing the direct total power loss are analysed for different conditions. Furthermore, the thermal effects on the oil film properties and lubrication mechanisms are calculated and discussed. This work provides sufficient methods and processes to evaluate the causes of the lubrication failure. It proves that the effects of heat exchange in the energy loss and efficiency loss between piston and cylinder are critical. Finally, some suggestions are given for a better design of the axial piston pump.