The cause of vibration noise of an axial piston pump is researched and analyzed. Vibration test of pump was carried out, the vibration testbed was set up and multipoint vibration power spectrum was tested. The theory pressure and flow pulsation, time domain and frequency domain characteristics of piston pump were analyzed. The structural modal simulation of pump was done as well. Through the comparison and analysis of experimental and simulation results, the source of the noise of pump and testbed system was located. The causes are identified and the noise control method is proposed.