Piston pump is easy to produce the local wear phenomena at operating temperature, according to the parameters of a certain type of radial piston pump the working temperature was calculated.Through the thermal deformation analysis of the circular and square section of the plunger and the guide hole, we get the relative thermal deformation of two different crosssection plunger and the guide hole was got. The analysis result shows that the relationship between the plunger and the guide hole square section can basically maintain a face to face contact during thermal deformation, this section plunger and the guide hole can be applied to piston pump.