To reveal the deformation regularity of tailor-welded tube (TWT) with dissimilar thickness during hydro-bugling, finite element analysis (FEA), experiment and mechanics analysis were conducted on the deformation behaviors of the thinner tube and the thicker tube, the initiation and expanding of the plastic deformation and the factors which affect bulging harmoniously. The effects of dissimilar thickness on the stress and strain history were analyzed. It is indicated that the deformation of thicker tube lags behind the thinner tube during bulging process. For the thinner tube, the plastic zone first occurs at the middle zone, and then expands towards two ends simultaneously. As for the thicker tube, the plastic zone first occurs at the end adjacent to the weld-seam, and then expands to another end gradually with the pressure increasing. The deformation compatibility can be improved with increasing the hardening exponent n and the length ratioη. No matter what the length ratio, the axial strain is tensile strain for the thinner tube, and compress strain for the thicker tube.