Abstract:Features of external gear pump are simple structure, light weight, high reliability, etc, it is widely used in hydraulic equipment. But the pump structure and working principle lead to trapped oil phenomenon, seriously affecting gear pump efficiency and stability. Trapped oil phenomenon and existing solutions were briefly described. The pressure distribution of gear pump was analyzed by simulation. The change of the trapped oil volume in gear pump operation stage was studied in detail. On this basis, a new method was proposed to solve the trapped oil problem.