River in mountain area has the characteristics of narrow waterway and fast flow,especially in the construction diversion narrows the channel’s width is as high as 60%-70%,which has a great influence on the changes of discharge capacity and the navigation flow condition.According to the basic hydraulics principles of energy equation and the relationship between flow resistance coefficient and flow capacity,we apply the approaches of cutting nozzle along the slope and leveling bottom to effectively reduce the resistance of the river shape and the roughness coefficient of the flow,and the approaches can enhance the discharge capacity of the river channel;we use the method of reducing the height of the narrowed bed for increasing the flow section to decrease flow rate and to increase maximum traffic flow;we take the measures of extending the various height’s point in diversion bed to upstream and downstream endpoint for the longitudinal cofferdam and connecting the bottom of the bed with a gentle slope,and the measures can reduce the rate of change of flow section,the height of water and the water flow,also improve the navigable condition.The results show that the proposed method is feasible to increase the discharge capacity of narrowed channel and the maximum traffic flow.