In the swabbing process of pumping unit, submergence depth is the one of principal elements that affects filling degree of sucker pump. Based on the one-dimension equation of fluid into the pump, gas state equation, fill factor equation, the solving model of filling degree of pump unit is established. Writing program with Visual Basic 6.0, the calculate simulation of performance to oil-well pump is explored. The results shows: submergence depth is increased, the filling degree and pressure in the pump also are increased and transient fluid-loss is decreased.