Abstract: Base on the copper foil tracer method,the parameters for friction stir spot welding 2mm-thick 6061-T6 aluminum alloy sheet was optimized.The influence of different plunge depths on the characteristic evolution and mechanical properties of joint interface was investigated by setting the geometric characteristic parameters of interface distortion.The experimental results reveal that the effect of plunge depth on the interface distortion morphology was most significant,comparing to other welding parameters.Increasing the plunge depth could almost eliminate the interface warping,increase the width of effective bonded area and shear strength of the joint.