Abstract: Shear stability experiments on aeronautic composite stiffened panel were conducted to investigate the buckling load, buckling mode, post-buckling carrying capacity and failure characterization. The results show the centric lines of buckling waves have an angle of 45° with the direction of stiffeners under shear buckling load. The re-buckling behaviors will occur when the buckling ratio reaches 1.2. Failure load is 1.28 times of the buckling load. The stiffeners work as 'skin buckling separated' before re-buckling, and have little deformation. Theoretical analysis on the buckling and post-buckling behaviors was carried out. The buckling load by theoretical analysis is in a good agreement with experimental results with an error of 7.2%. Additionally, the slope of load-strain curve in post-buckling stage by theoretical analysis also leads an error less than 10% compared with experimental data. Finally, the variation law of the post-buckling angle and buckling ratio was determined.