Abstract: In order to study the tensile stress state of an aluminum alloy sheet welded by friction stir welding in airplane, three models of welded sheets which were distinguished by weld geometrical type of plane, protrude, concave were built in ANSYS' preprocessor. In each model, a symmetrical constraint condition was acted on the left end surface while a tensile stress was loaded on the right. A numerical simulation result was obtained with such conditions after ANSYS' solution.The result shows that the stress concentration of the welds depend on their geometrical shapes.If the model is concave or protrude, the eccentric bending caused by the tensile stress will affect the distribution of the stress.Especially if the model is concave, the eccentric bending will make the stress concentration sharp in the weld area and the deflection obvious in the end surface of the sheet.