An analytical solution for the buckling and postbuckling behavior of stiffened arbitrary laminated composite panels is presented. The stiffened composite panels are modeled as panels with elastic restrains. The analytical formulations for the buckling and the postbuckling behavior subjected to compression, shear as well as combined compression and shear loads are derived by constructing the deflection function and using Galerkin method. Nondimensional parameters are introduced to express the solution in a simple formulation. The initial imperfections and prebuckling deflection are considered to predict the postbuckling behavior more exactly. Comparisons of the finite element method (FEM) are conducted to evaluate the effect of the geometric parameters, spring stiffness, etc. Considering the web of stiffener reinforced to the panels, the averaged stiffness method is applied to the buckling and postbuckling analysis of composite panels with T-shaped stiffener. Compared with analytical simplified models and FEM results for the stiffened composite panels with T-shaped stiffeners, the good accuracy of the averaged stiffness methods in predicting the buckling and postbuckling behavior is demonstrated.