In order to solve the problem in digital design of swashplate axial piston pump under the fluidstructure interaction (FSI) conditions, a compute fluid dynamics method (CFD) based on dynamic boundary was used for its modeling and decoupling analysis. UG was used to build the three dimensional (3D) model of fluid in piston pump during working process, gambit software was used to mesh the fluid model and to localize in detail, and fluid boundary was set as dynamic boundary. Methods of UDF function in Fluent software were used to define the viscosity and compressibility of fluid, and the rules of motion of boundary. Digital model was established and analyzed with simulation to obtain the rules of variation of the pump outlet flow by the FSI conditions. Finally, an experimental platform was designed and built to measure the outlet flow and outlet pressure of piston pump. By comparing the simulation data and experimental data, the experimental result demonstrates the feasibility and correctness of this method of modeling and analysis.