Reasonable selection of gear’〖KG-*2〗s displacement coefficient is an effective measure to reduce trapped oil volume and flow pulsation. In order to specifically analyze the influence of the displacement coefficient on the trapped oil volume and flow pulsation coefficient of the internal gear pump, a numerical model of the involute internal gear pump was established according to the meshing theorem. Then the trapped oil volume and instantaneous flow rate of the internal gear pump were solved using the swept area method, and finally the influence of the trapped oil volume and flow pulsation with the variation of the displacement coefficient was analyzed. The results show that: in the case of other parameters remain unchanged, with the increase of the pinion displacement coefficient, the trapped oil volume first decreases then increases, the instantaneous flow rate gradually increases and the flow pulsation rate decreases.