Gear pump is formed by relying on the pump cylinder and the meshing gear working volume change and move to pump fluid or pressurization of the rotary pump. By two gear, pump body and cover of two closed space, when gears, gear side space volume from small greaten, forming a vacuum, the liquid suction, the side of the gear mesh from large to small volume of the space, and the liquid into line. Suction chamber and discharge chamber are separated by two gears meshing line. The gear pump outlet pressure depends on the size of the source resistance pump.