A thermodynamic lumped parameter model for oil film in slipper pair clearance of axial piston pump is constructed by means of the control volume method on the basis of the law of conservation of energy, and the instantaneous temperature of oil film is thus solved. The results show that the shaft work losses of slipper pair are positively correlated with the piston chamber pressure and the cylinder speed, and the losses are converted into heat energy; and that, the increase of internal energy of oil causes oil temperature to rise and changes the heat transfer rate between slipper pair and oil film. In addition, the multi-element complex brass is selected as the material of slipper, because it has a high thermal conductivity and a low thermal resistance, which results in good heat dissipation and excellent wear resistance.