Abstract: In order to investigate the forming limit of tailor welded blanks(TWBs) with different thicknesses low carbon steel(ST16) sheets with thicknesses of 0.8 mm,1.2 mm and 1.5 mm were welded together with the thickness combinations of 0.8 mm/1.2 mm,1.2 mm/1.5 mm,and 0.8 mm/1.5 mm.The forming limit (FL) of three base materials and three TWBs were got from experiments.The difference of the FL between base metal and TWBs was compared and the effect of the thickness combination rate was studied.Results show that the forming limit of TWBs with different thicknesses was less than that of the base material and was determined by the thin base blank.The strain gradient along the welded line increased with the thickness combination rate increase.