Usually, in the process of cured stringer co-bonding with uncured skin for composite stiffened panel, the fiber of the skin at the edge of the stringer flange will be buckling due to the bridging of auxiliary materials. According for these, this article studied that how the angle of chamfering at the edge of the stringer, skin thickness and skin ply angle influence the buckling of fiber in the skin nearing the edge of the stringer flange. The reason and mechanism of fiber buckling also were analyzed. The results show that decreasing the angle of chamfering at the edge of the stringer is beneficial to reduce the buckling degree of skin fiber. At the same time, the fiber buckling degree is positively correlated with the skin thickness, and negatively correlated with the 90 ° ply ratio in the skin ply. In engineering application, proper chamfering of stringer edge is beneficial to improve the forming quality for composite stiffened panel without using the craft soft cover.