This paper discusses the clearance leakage and friction torque changes of slipper pair in axial pistonpump with different cylinder speeds,different cylinder pressures and different centrifugal force arm sizes.The resultsshow that ( 1) the cylinder speed,the cylinder pressure and the centrifugal force arm size are important parametersaffecting the clearance leakage of slipper pair which are related to pressing force,dynamic-pressure effectand centrifugal moment of slipper; ( 2) the friction torque increases with the increase of clearance leakage; ( 3) theactual clearance leakage and friction torque loss of piston pump increase as cylinder pressure and speed increase,and they are greater than their theoretical value due to the effects of piston pair and valve plate pair; and ( 4) theclearance leakage and friction torque loss of slipper have smaller effect on the volumetric efficiency and mechanical efficiency of axial piston pump.