Abstract: Aircraft structures of advanced composites are usually designed to post-buckling stage so that the most loading capability could be yielded. For the problem of post-buckling of composite stiffened plate structures, the self-developed program was introduced, which was embedded into software Patran as processing and post processing. The static buckling mode was calculated by this self-developed program, and then the mode was assumed as the initiation deflection for calculating post-buckling. The nonlinear equations were solved by increment iterative, arc-length control and energy convergence criterion. Introducing Tsai-Hill criterion of composite materials failure, the damage information of elements were judged and degraded. The self-developed program was verified by the compression test of composite stiffened plate. The post-buckling capacities of composite wing boxes were calculated and experimentally carried out in different cases such as loading and materials choosing, and the numerical results were in good agreement with the test data.