Based on the brief introduction of the structure characteristics and development direction for the existing crescent gear pump, the necessity of improvement and optimization with strcture for crescent gear pump was pointed out. Therefor, the new double internal gear electric motor pump with three idlers was proposed as an innovative structure of gear pump. The hydraulic pressure of annular gear and sealing block was analysed based on dual three idler crescent gear pump, and it was concluded that the radial hydraulic pressure resultant force upon the annular gear and sealing block was zero, namely the balance of radial hydraulic pressure, which was helpful to improve the running smoothness of the pump and lifespan of pump bearing. Then the finite element method (FEM) was used to analyze the mechanical properties of meshing gear. The results show that under the ideal fluid pressure which is 12.5 MPa, the maximum stress of inner gear ring is 68.8 MPa and the maximum deformation is 0.008 mm, the maximum stress of engaging force is 131.1 MPa and the maximum deformation is 0.02 mm. The guide is provided for the design of structure parameters for dual three idler crescent gear pump such as number of teeth, modulu and pressure angle, and etc.