Through the integral model test of the Rumei Hydropower Station, characteristics of flow pattern, water cushion depth, hydrodynamic pressure and velocity distribution at the downstream channel were studied. Optimization schemes of adding a subsidiary dam and lowering the bottom elevation of the plunge pool were compared. The results show that the effect of adding a subsidiary dam downstream the plunge pool is closely related to the height of the subsidiary dam, the discharge and the width of the valley, and can worsen the joint of the outflow and the downstream channel. Lowering the bottom elevation of the plunge pool has little influence on the downstream connection, and it can effectively increase the depth of the water cushion and reduce the near-bottom hydraulic indexes of the plunge pool.