An axial piston pump is a positive displacement pump with a plurality of pistons in a circular arrangement in the cylinder block. It can be used as independent pump, hydraulic motor or automobile air conditioning compressor. An axial piston pump has a plurality of pistons arranged in a circular array within the housing of the cylinder block, rotor, or cylinder. The cylinder is driven by an integral shaft more or less aligned with the pumping piston to rotate about its axis of symmetry. In this article, we mainly introduce the working principle of piston pump.