Abstract This work considers the postbuckling behaviors of Functionally Graded Material (FGM) plate in hygrothermal environments. Basically, the structures change continuously in the thickness direction according to the volume fractions of the material. For the description of the model, the first-order shear deformation theory (FSDT) is used, and von Karman strain–displacement relations are applied. In the analysis, finite element method and Newton–Raphson technique are adopted to analyze the thermal postbuckling behavior of the model. Furthermore, a simple power-law is employed in the thickness direction of the plate, and the temperature and moisture effects are fully investigated in this study. To check the validity of the present work, comparisons with the previous results are performed. And then, moisture effects on the model are significantly appeared due to the increase of the volume fraction index of the materials.