A plate structure is a structure made up of several plates. To solve the bending problem of orthotropic plate, a general analytical solution of partial differential equation for transverse displacement function of orthotropic rectangular plates in bending must be worked out. It can be used to solve the bending problem for arbitrary boundaries and arbitrary load. For each plate; some edges are independent which can be calculated by boundary conditions, while some edges are connected by other plates which can be calculated by continuous conditions. With the equations made up of these conditions, it can be used to solve all the integral constants in general solutions. For example, a water tank under hydrostatic pressure with the edges simply supported at the top and fixed at the bottom has been calculated.