Laminated glasses are widely used in the ship bridge windows and portholes because of its characteristics of the good impact resistance and anti-fragmentation. However, it is easy to be broken due to waves and wind, which affects the navigation and operation of ships. In order to verify the equivalent thickness formula of the laminated glass in the current rules and regulations, the displacement function is solved by the Navier method according to the classical bending theory of the composite laminates. The normal stress of the laminated glass is then obtained and the new equivalent thickness formula of the laminated glass is derived without considering the transverse shear deformation. Abaqus is used to carry out the linear and nonlinear numerical simulation of the equivalent single-layer glass plate and the laminated glass plate, respectively. The comparison between the numerical results of finite element method and the theoretical value shows that the new equivalent thickness formula has higher accuracy than the equivalent thickness formula in the current rules and regulations.