In order to achieve the output flow change in grading of gear pump, the gear motor output torque and rotational speed changes in grading, the inner and outer meshing gear pump and motor was designed, and a drive system combined of the internal and external meshing gear pump and motor was made. By taking the type of inner 3 outer 2 as an example, the principle of internal and external meshing gear pump and motor were analyzed. The pump had five independent oil outlets, 11 different ways of oil supply could be formed through different combinations. The motor had 5 oil inlets, and they coud output 11 kinds of torque and rotational speed under a common connection, but 6 kinds of torque and rotational speed under differential connection. The analysis results show that in the drive system of internal and external meshing gear pump and motor, the motor torque and rotational speed grading can be changed by changing the oil pump combination and the connection way of the motor, which will widen the field of gear pump and the motor adaptation.