Abstract: According to the Reddy's higher-order shear deformation theory,geometrically nonlinear governing equations and their boundary conditions of laminated composite plates,including the hygrothermal effects,are obtained by the virtual displacement principle.The boundary conditions are elastic restraint against rotation.Specification between simply supported and clamped boundary conditions can be acquired using different elastic coefficients.It is assumed that the material properties are not affected by variation of temperature and moisture.The governing equations are solved by Galerkin method.Four clamped edges are assumed in numerical analysis.The factors of hygrothermal environments,length-thickness ratios,aspect ratios and total number of plies are discussed.Results show that temperature rise leads to disadvantageous effect on the bending behavior of composite laminated plates,but the effect of moisture is insignificant.Increase of the number of plies will lead to evident decrease of bending deflection and moment or bending stress if other geometrical conditions remain unchanged.