Abstract: The finite element software was used to analyze the shear strength and failure mechanism of X-cor sandwich structure. During the shear strength analysis, the failure criterion and materials stiffness degradation rules were proposed, and the failure process and modes of X-cor sandwich structure were also clarified. According to the failure criterion, the elements with stiffness degradation and their distributions in the finite element model were used to simulate the types and propagation path of the failure. And the failure mechanism of X-cor sandwich was explained. The results show that under shear load the resin regions fail first; and then the multiple failure modes of Z-pin pull-out from the face-sheet, Z-pin shear off and Z-pin buckling appeared. The finite element results were consistent well with the values of test result after comparison, which meant that the failure criterion and stiffness degradation rules were effective.