The gate type of Panghai ship lock is flat,and the working head is 23.0 m.The initial submerged depth of gallery roof is only 7.5 m,and the hydraulic problem on the flat gate is the key technical problem in hydraulic design.Based on physical model researches,twe propose to expand the corridor,optimize the gate structure and corridor structure,and discuss the cavitation and hydraulic characteristics.Research shows that,cavitation problems could be solved on the basis of optimizing the gate structure and corridor structure,applying the techniques of extended corridor type,and take the necessary measure,natural aeration by lintel,and reserve measure,forced aeration by the drop floor.