The working mechanism of the stationary crescent for radial compensation of the inner mesh gear pumps is studied and the model was established.Then the force of the above and below stationary crescent during the process of operation and the changing cycle of hydraulic pressure are analyzed.The distribution of pressure on the above and below stationary crescent in different positions and the hydraulic force at the x、y direction are determined.The rotational angle of the maximal force of the above and below stationary crescent and the constraint conditions of the two stationary crescents stay close to the crest of inner gear and external gear to form radial seal are obtained.The angle of the end of the above stationary crescent in the high pressure area and the fixing angle of the seal stick of the least resultant force is calculated by optimization.