Abstract: Focusing on the various cross-section forms of the main beam and the unreasonable value of the beam height of the steel gate under middle and low water head, the characteristic expression of the I-shaped equivalent composite section and the stress model of the main beam are established. The result shows that the stress and deflection of the gate under the effect of water pressure, self weight and other loads is inversely proportional to the third power of the height. Therefore, with the help of finite element analysis method, optimization solution of the beam height is proposed through the case in which distributions of stress, deformation and weight changes of the gate under different working conditions are compared.