Plunger adhering phenomenon of the swashplate axial piston pump used in excavator often causes the piston pump slipper to fall off and return tray to break,which makes the pump unable to work.To solve this problem,it is necessary to study the optimum clearance between piston and cylinder block.Taking the piston pump with 112 mL/r displacement as an example,the pressure deformation,thermal deformation and thermo-mechanical coupling deformation of the cylinder block and piston with different piston pair clearance values were simulated and analyzed by ANSYS-Workbench software to study the influence of different piston pair clearance values on the volume efficiency of the pump.By analyzing,the recommended clearance value between piston and cylinder barrel was propose.It is proved by experiment that the pump will not cause “stuck” and its volumetric efficiency can reach 96%~97%.This study provides reference for choosing the best clearance of different swashplate axial piston pumps.