In order to increase decision accuracy of the intermixing slab length and position, and decrease the slabs which are offgraded or scrapped. Water model experiments were conducted to simulate the continuous casting grade transition process of No. 2 continuous caster at Bao Steel. The dimensionless concentration profiles along slab length with different continuous casting conditions were measured. Based on the profiles a mathematical model was developed to predict the final composition distributions and length of intermixing slab. Comparison of predicted dimensionless concentration profile with plant data shows that the precision of the model is considerably satisfied to meet the need of steel grade transition evaluation.