Abstract: FEM was utilized on the aluminum alloy flat buttdwelded joint with ABAQUS software and the effects of HAZ geometrical dimension on aluminum alloy joint's deformation and strength were studied.The results indicate that with the increasing of HAZ's length,the yield stress and tensile stress of the joints both decrease gradually.The stress traxiality lays mutation between the base material and HAZ and between the weld metal and HAZ.At the same time,the position of the maximum stress traxiality is from the boundary between the base material and HAZ to the boundary between the weld metal and HAZ.With the increasing of thickness of joint,both the yield stress and tensile stress of the joints increase gradually.The stress traxiality of the joints depends on the thickness of specimen,dimension of weld metal and dimension of HAZ.With the increasing of width and gauge of joints,the yield stress,the tensile stress and the maximum stress traxiality increase basically.When the gauge of joints increases to certain value,the yield stress,the tensile stress and the maximum stress traxiality remain constant basically.