The downstream tail water level of Changsha Hub is far lower than the designed minimum water level in the dry season.In order to analyze its impact and study countermeasures，this paper adopts methods such as data statistics and analysis，comprehensively analyzes the impact of downstream low water level and corresponding water head parameters on the operation of the hub dam，navigation of the ship lock and operation of the power station，and proposes countermeasures as follow.The original maximum working head of the dam should be raised from 9.3 m to 11.2 m.The minimum ecological flow of 348 m3s should be ensured through hub short-term dispatching and basin joint dispatching.“Segmentation，zoning，orderliness，time control，and quantity limit” should be adopted to comprehensively control sand mining in the downstream river channel.“More holes and less flow” should be adopted to release water，and underwater photography and dam safety monitoring should be adopted regularly to ensure dam safety.To prevent the ship from stranding，the water conveyance valve of the ship lock should be opened in a way of “first slow and then fast” to ensure the safety of the mooring line when the floating bollard hits the bottom.A 3000-ton three-line ship lock should be built to ensure the safe navigation of the ship lock.The unit should operate under the operating water head of 7.0 m，and the unit should not be started when the downstream water level is lower than 19.55 m.The forebay of the power station should be cleaned in time to ensure the safe operation of the power station.