According to the unsteady flow of the K3V axial piston pump, the flow field of the K3V axial piston pump was analyzed by CFD software. The rotatory movement of the piston pump block and the rectilinear movement of the piston were dynamically simulated on the base of sliding mesh and dynamic mesh. The pressure contour of the piston pump oil-film, the flow rate curve of the pump outlet and pressure curve of the piston cavity were gained. The phenomenon of flow backward was analyzed.The research provides theoretical basis for the design of the K3V axial piston pump channel.