Abstract: The surface and corner cracks of continuous casting billet form during the continuous casting process, especially in medium-carbon steel. Surface defects of such billets are directly related to the secondary cooling process of continuous casting, while the center deviation of the billet, center shrinkage, and center loosening in medium-carbon steel, medium-carbon alloy steel, and high-carbon steel are especially prominent. Such quality defects are related to the secondary cooling and press-down process of continuous casting. These two defects are the main factors restricting continuous casting production. The secondary cooling of the continuous casting process has an important influence on the surface and internal quality of the slab, especially the temperature of the slab corners, which directly affects the surface quality of the slab. Under the existing process conditions, the mathematical model for calculating the solidification heat transfer of the slab in the secondary cooling zone is calibrated and improved, and a three-dimensional secondary cooling model is developed to solve the influence of uneven cooling due to water distribution on the temperature of the slab. This controls the surface quality of the slab, especially the corner cracks of the slab, and improves and optimizes the slab continuous casting secondary cooling system to improve the slab quality. An equation for calculating the soft reduction parameters is proposed, and the existing soft reduction process is optimized by combining the developed three-dimensional secondary cooling model with the proposed and applied controllable single-stage soft reduction and unsteady soft reduction control to solve the internal quality problems, such as central segregation, central porosity, and shrinkage of the continuous casting slab. At the same time, the model database is optimized to make the data more complete and the model calculation more accurate. This model adds the technology of mixed casting of different grades of steel and the technology of predicting and controlling the W-shaped solidification to further improve the applicability and accuracy of the model. The model has been developed and successfully applied in several steel plants, and the result shows that the proposed model can improve the surface and internal quality of cast slabs effectively, such as cracks and segregation.