At the miter gate of large-scale ship lock,buoyancy tank is usually set to improve the stress state of operating parts of the top and bottom pivot,and to reduce the drooping volume of gate head.First of all,seven kinds of different buoyancy tanks of the rectangle,U type,⊥ type,L type,J type,T type and Π type were compared under the same buoyancy to analyze the features of bearing reaction of top and bottom pivot,drooping volume of gate head,natural frequency and ventilation path,and give a relative reasonable structural form of buoyancy tank.On this basis,five kinds of buoyancy tanks of one layer,one and a half layer,two layers,three layers,and four layers with different buoyancy forces were compared to analyze and give a relatively reasonable control range for the buoyancy force of buoyancy tank.