Abstract: The shear properties of composite stiffened panel with cover were investigated through tests and finite element methods. Based on the finite element model of composite stiffened panel with cover and by removing cover, the finite element simulation analysis was conducted on large opening composite stiffened panel without cover to investigate the effects of cover on composite stiffened panel with cover. Test and numerical calculation results reflect that different regions of composite stiffened panel with cover buckles simultaneously and the final failure position is at the composite panel area outside the stiffeners. When the cover is removed, the rigidity and load-carrying capacity of structure get reduced, and the stress concentration point and location of the initial damage of structure both get shifted. The failure modes show no obvious change when failure, both are local buckling.