In order to study the cavitation characteristics of a water hydraulic axial piston pump, cavitating flow in the pump was simulated based on Schnerr—Sauer model. The fluctuations of flow and pressure at the outlet of the pump were analyzed at different inlet pressure conditions. From the simulation results, it is concluded that obvious cavitations occur in the cylinder chambers which are in suction process. Cavitation regions are mainly located in the sides near to the rotation center, and more serious cavitations occur in the piston chamber which contact with the suction side of the portplate. Dynamic pulsation of flow rate and pressure at the outlet of pump are more severe when serious cavitations occur. Cavitations can be reduced if the pressure at the inlet of pump is increased, but excessive pressure at the inlet can induce pressure pulse in piston chamber which in suction region. When cavitations are decreased to some degree, dynamic pulsation of flow rate and pressure of pump can not be impacted obviously by the pressure at the inlet.