Both experimental and mechanical analyses were carried out to investigate the characteristics of thickness distribution for tailor-welded tube (TWT) hydroforming with dissimilar thickness.Then,the effects of weld-seam position and thickness difference were also revealed.A multiple-diameter tube was formed to reveal the characteristics and the regularity of thickness distribution during TWT hydroforming.It is indicated that there are obvious fluctuations in thickness distribution though the TWTs have the same expansion ratio.The thinning ratio of thinner tube is bigger than that of thicker tube especially in the zone closed to the weld-seam.The difference in thinning ratio between two tube segments can reach 9％.Consequently,sudden and large fluctuation of thickness appears in the zone nearby the weld-seam.The difference in thinning ratio between thinner and thicker tubes enlarges as the thickness difference increases,but improves as length ratio increases.Different strain states are the main reason to induce nonuniform thickness distribution.The difference in thickness is the main reason to induce different strain states on thinner and thicker tubes.