Tailor welded blanks had been widely used in automobile industries. In this paper, the formability of tailor-welded blanks with curved seams had been studied in experiments, and compared with that of tailor-welded blanks with straight seams. For tailor welded blanks with curved welded seams, the effects of thickness ratio on the limited forming height are the same under various welded seam shape, and the limited forming heights are decreased and then increased with the increase of thickness ratio, which different to that obtained from tailor-welded blanks with straight seam. The reasons that the shapes of welded seam how to influence the formability of tailor welded blank are deduced in the paper. Results show that the shape of the welded seam can change the blank’s deformation condition, which one of the main factors of determining the sheets formability.