Abstract: To analyze the influence of side boundary condition on the compression stability performance of composite stiffened panel, finite element software was adopted firstly for modeling and numerically simulating of composite stiffened panel under axial compression to obtain the buckling load and buckling pattern of the panel with unloaded edges simply-supported or unsupported. Then, load carrying capacity of the panel was estimated by engineering calculation method. According to the calculation results, axial compression tests on composite stiffened panels were conducted to analyze the influence of side boundary condition on the buckling pattern, buckling load and post-buckling failure process of the specimen. Test results show that, side boundary condition affects the buckling pattern as well as failure pattern of the stiffened panel. For specimens with unloaded edges supported, the overall deformation after the buckling is slight and the main failure pattern is the compression fracture of stiffeners. For specimens with unloaded edges unsupported, debonding and bending fracture of stiffeners caused by overall deformation after buckling are the main failure patterns, and the debonding of stiffeners decreases the carrying capacity of the structure obviously. Finite element calculation results accord with the test results well, which validate the rationality of the finite element model. It is of preferable accuracy to estimate the carrying capacity of stiffened panels with unloaded edges simply-supported by engineering calculation method.