Abstract: The tensile behavior of T-joints consisting of integral composite honeycomb sandwich structure is studied by experiment. The strength and failure modes of such elements are both obtained. An FEM model of the joint is then established. The classified damage criterion, failure criterion, and stiffness degradation rules are applied in order to simulate the damage and the tensile properties of the joint. The result of the FEM model shows good correlation with those from experiments. Results have shown that the weak point of the structure is on the end of web panel near to the skin panel. Out-of-plane fracture of the honeycomb in this area leads to the final failure of the structure. Tensile load on the web panel is transmitted to the skin panel mainly through the transition area, while the lapping zone between the web panel and the skin panel contributes less to the transmission. Parameter studies show that the length of the lapping zone has marginal effects on the strength of the structure, while thickening the skin`s honeycomb or employing honeycombs with a lower modulus can increase the strength.