The pressure-compensated plunger pump can better adapt to the extreme deep water environment, but the extreme deep water environment will change the lubrication characteristics of the plunger pair, affecting its underwater working performance and application range. Taking the lubrication characteristics of the auxiliary oil film of the plunger of the pressure compensation pump as the research object, considers the influence of environmental factors such as deep water temperature and pressure on the viscosity, density and other media properties, establishes a numerical model of the auxiliary oil film of the plunger in the deep water environment, and proposes the In the eccentric direction, the method of coordinate rotation optimization and finite difference discretization is used to solve the parameters that characterize the lubrication characteristics such as the thickness of the plunger pair. The results show that when the water depth is 1000m and the rotation angle of the main shaft is about 90o, the secondary oil film of the plunger appears in an extremely thin area less than 1μm, and the pressure difference reaches 80MPa. When changing the spindle speed and the inclination angle of the swash plate, the leakage and axial friction changes more significantly under air conditions. Under different water depths, there is a positive correlation between the axial friction and the water depth, but the change in leakage is the opposite. Related research can provide a useful reference for the design and development of pump plunger pairs in deep water environments.