To study the fluid character of axial piston pump, a mathematical model of flow condition in piston chamber was developed with compressibility of fluid oil. The model was further improved by analysis of movement model of piston, cross area of valve plate, throttle coefficient, flow loss inside pump, etc. Besides, the m odel of whole piston pump with its hydraulic system was developed with lamped pa rameter method. A simulation system was built by using Matlab based on the mathe mat ical pump model. A visual graphical user interface was established to automatica lly analyze the relation between pump geometric structure, working conditions, s ystem parameters and flow conditions of pump. The flow conditions of the pump we re tested by using pump flow ripple test rig. It is shown that the pressure puls ati on and flow ripple results calculated by the mathematical model agree well with the experimental results. The analytical error can be controlled within 5%. It c an be concluded that the developed mathematical model has high precision and can accurately predict the fluid character of axial piston pump.