Based on the test data of a repairing gate installed on the middle outlet of Jiangkou Hydropower Station, some researches about hydraulic properties of an inclined gate slot under high water head were conducted.Study contents included flow cavitation characteristics, gate closing?speed, configuration of gate bottom, wind speed in the vent and gate olding?force in process of gate closed in flowing water. The test data indicated that the arrangement of the repairing slot of the middle outlet can meet the requirements recommended by China's high pressure gate design criterion; when the gate is fully opened under the design water level, the flow cavitation numbers of slot section are 0.8～0.9 and no cavitation happened. In order to solve the problem of impact?force change due to water jetting on inclined slots, it is necessary to increase the interleaving?platform size properly. A kind of configuration of the gate bottom described in the fifth scheme was recommended.