The research aims to investigate the failure behaviors of the composite sandwich structures with debond defect subjected to compression loading. Experimental results revealed that the sandwich structures with either thick face-sheet or short debonded length exhibit higher failure strength. Moreover, when the debonded length is short, the failure is dominated by global buckling followed by core failure. Nevertheless, when the debonded length is long, the failure mechanism becomes the local buckling followed by the crack extension from the debond defect tip. The nonlinear finite element simulation was performed on the sandwich samples for the failure analysis. It was found that when the failure is dominated by the global buckling, the strength can be characterized using the maximum principal strain criterion. On the other hand, when the failure mode is local buckling, the failure strength can be predicted using the damage zone method.