Abstract: Internal gear pump are widely used in industrial practice, and the lubrication performance between stationary crescent and external gear play an important role for such kind of gear pump. A calculating model was established for calculating the lubrication performance between stationary crescent and tooth surface. And based on this model and by numerical simulation, the model LL4724 internal gear pump was taken as the example to research the oil film pressure distribution and the influences of gap between stationary crescent and external gear, rotation speed of small gear on the film pressure, friction force and the circumferential flow rate of the gear pump. A series of performance influence curves were obtained and explained.