Stormwater drainage system with pumping is a common configuration in area where the receiving water level is much higher than pumping station wet well levels. Because of high water table or sewer cross connection, the stormwater sewers are fully or partially stored with infiltrated groundwater or foul water in dry days. Discharging the stored water before storm event is an important operation pattern of pumping station, in order to make room for collecting and conveying the wet weather runoff inflow. The operation pattern analysis needs was discussed with information collection requirements, pump schedule strategies and sewer storage volume calculation. Taking a small stormwater drainage system as a case, the schedule of pump starts, the pumping water volume and pumping duration under two typical operation patterns were studied. The drainage system model with pumping and the quantity analyses of discharging dry weather stored water are valuable for pumping station operation associated with precipitation forecasting.