Abstract: Based on stress inheriting characteristic of the billet shell in continuous casting,a thermo-mechanical coupling model of billet is established.Heat transfer and stress fields of the billet in the mould is analyzed by the finite element software ANSYS.The mould taper is optimized according to principle of minimum air gap and the influence of single-taper and multi-taper on solidification behavior of the billet shell in the mould is analyzed.The results show that under these two tapers,the solidification behaviors are obviously different in the corner area of the billet but basically the same in the central area.In the single-taper mould,the air gap spreads widely and heat flow remarkably reduces in the corner area;"hot spots" appear at the area around 12~22 mm away from the corner.In the multi-taper mould,the width and distribution of air gap significantly decrease and there are no "hot spots" in existence,which demonstrates multi-taper mould is more consistent with the solidification shrinkage law of the billet shell.