In this present study, we are interested in the use of a precise theory of shear deformation for the buckling analysis of plates with functional gradation simply supported such as the refined theory of plates with four variables, several parameters of comparison have been used, dimensional and non-dimensional, the displacement field is compatible with this study, the non-use of shear correction factors is satisfied, the choice of material is very precise in such a way are variable according to the thickness of the plate and on the other hand to make comparison with other researcher and confirms that this study gives precise results and converges, the transverse shear stresses vary through the thickness, the results found is also studied and discussed.