Abstract: In order to control surface cracks in blank beam during continuous casting process,the thermomechanical coupling model of heat transfer,solidification and shrinkage of slab in mold was established by using multi-load step method.According to the calculation results about air gap,based on the principle of air gap minimization,the single taper is optimized for each surface of the beam blank and the best scheme of single taper optimization is determined. After twice optimization on taper,ie,the taper of flange tip is 0.81%/m,the taper of narrow face is 0.38%/m; the taper of-1.44%/m is relatively appropriate for the fillet and flange.The calculation result indicates that the large taper of the mold is the main cause for generating the surface crack,and then it is recommended to reduce the taper.