Abstract: With the large-scale acceptance of new energy by the power grid, hydropower is faced with higher intensity peak shaving and frequency modulation tasks.Especially in the "one leading reservoir with multiple stages" hydropower station group, it is easy to cause the fluctuation and instability of water level in daily regulation power station and lead to frequent adjustment of gate opening.The traditional gate application method based on artificial experiences cannot meet the requirements of water level regulation accuracy and decision-making efficiency.Therefore, a combined optimization application model of cascade hydropower station group gates, which combines "offline calculation" and "online search", was proposed.Firstly, the feasible gate opening combination scheme under different water levels of each hydropower station was calculated offline, and the master table of cascade gate operation strategy was constructed.Then, the optimal gate opening combination strategy was searched online according to different control objectives such as minimal surplus water, water level control, water level stability, less adjustment of gates and discharge stability.Taking four hydropower stations in the middle reaches of the Dadu River, Pubugou, Shenxigou, Zhentouba and Shanan, as examples, the results showed that on the premise of completing the water level control targets of the leading hydropower station Pubugou Hydropower Station, the total number of gates used in the cascade power stations were effectively reduced by 59.1%.The fluctuation amplitude of the water level in the three downstream daily regulating or runoff hydropower stations, Shenxigou, Zhentouba and Shanan, decreased by 1.5, 0.8 m and 1.0 m respectively.The difference coefficient of the discharge flow of Zhentouba hydropower station was reduced by 0.02.It has realized the optimal use of the hydropower station group gates under the condition of high intensity peak shaving and frequency modulation, and has improved the safety and scientific level of the hydropower station group dispatching decision.