The mechanics behaviour of connecting frame in aircraft composite cabin under static load can be expatiated through its dangerous key components. Initial damage and ultimate strength of the key component are studied using progressive damage method. Based on the strength prediction technique, the effects of composites ply angle and the structural layout on structural initial damage and ultimate failure are discussed to exploit the potential composite structural load carry ability. The numerical results show the ply angle modification can provide 26.3% increase on initial failure stress and 14.1% on ultimate strength. Farther structural layout adjustment can significantly increase the ultimate strength whereas go against the initial failure strength. The design scheme with concave boxes to cope with assembly demands is verified to be practical in joint structures by comparing with a connecting frame without concave boxes.