The objective of this study is to model and simulate the nonlinear lubrication performance of the slidingpart between the piston and cylinder wall in a hydrostatic swash-plate-type axial piston pump. A numericalalgorithm is developed that facilitates simultaneous calculation of the rotating body motion and fluid film pressureto observe the fluid film geometry and power loss. It is assumed that solid asperity contact, so-called mixedlubrication in this study, invariably occurs in the swash-plate-type axial piston pump, which produces a higherlateral moment on the pistons than other types of hydrostatic machines. Two comparative mixed lubrication models,rigid and elastic, are used to determine the reaction force and sliding friction. The rigid model does not allowany elastic deformation in the partial lubrication area. The patch shapes, reactive forces, and virtual local elasticdeformation in the partial lubrication area are obtained in the elastic contact model using a simple Hertz contacttheory. The calculation results show that a higher reaction force and friction loss are obtained in the rigid model,indicating that solid deformation is a significant factor on the lubrication characteristics of the reciprocating pistonpart.