This paper investigates the thermal buckling of laminated composite plates based on a refined plate theory that incorporates four variables, using hyperbolic and polynomial shear strain functions for the first time to analyze thermal buckling of a laminated plate with all edges simply supported. The proposed shear function incorporates the variation of transverse shear stress over the thickness of the plate in a parabolic form and achieves zero traction on the upper and bottom surfaces of the plate without implementing a shear correction factor. Equations of motion are derived according to the principle of virtual displacement. The analytical solution is carried out using Navier’s solution. The numerical results of the orthotropic properties of both cross-ply and angle-ply laminates are calculated by programming a MATLAB code. In the present study, the influence of changing various design parameters, such as aspect ratio (a/b), orthotropic ratio (E₁/E₂), thickness ratio (a/h), and thermal expansion coefficient ratio (α₂/ α₁), for symmetric and antisymmetric laminated composite plates is analyzed. The results are evaluated by the assumption of uniform temperature variation through the plate, which exhibits good agreement for both thick and thin plates compared with previous studies.