The influence of the hygrothermal effect is considered in the constitutive relation of carbon fiber reinforced composite (CFRP) based Reddy’s high-order shear deformation theory. The geometric nonlinear governing equations are derived by using virtual displacement method; and the boundary conditions are elastic restraint against rotation. Then, the physical parameters of CFRP are considered as constant in the hygrothermal effect, and the governing equations are solved by using Galerkin method, where clamped rectangular CFRP laminate is used. Finally, the effects of the different hygrothermal effect, length height ratio, length width ratio and total number of plies are discussed on the load-central deflection and bending moment.