Abstract: For the problem of center segregation and loose in rectangular continuous casting billets with a cross-section of 320 mm×480 mm, combined with the continuous casting process conditions of rectangular billet of a certain factory, a three-dimensional mathematical model of thermodynamic coupling in the soft reduction process of rectangular billet continuous casting was established. The influence of continuous casting reduction amount and reduction interval on the reduction effect of rectangular billet was simulated and analyzed. Based on this, some suggestions for optimizing the soft reduction process were proposed. The results show that the plastic strain of the slab is mainly distributed at the position of ±30 mm in the longitudinal center, which has a great relationship with the solid phase ratio at the time of reduction. when other conditions are constant, the greater the amount of reduction, the greater the equivalent plastic strain, When the amount of reduction is 11 mm, the equivalent plastic strain is 0.035. The greater the reduction amount, the greater the longitudinal displacement of the slab center, and the greater the corresponding deformation of the core of the slab. When the reduction interval is 0.3–0.9 and 0.7–1.0, the equivalent plastic strain of the casting billet core becomes 0.024–0.026, and when the reduction interval is 0.1–0.8, the equivalent plastic strain of the casting billet core is almost zero, so the reduction interval cannot be less than the solid phase rate of 0.1–0.8. It is recommended to consider the influence of process parameters such as reduction amount and reduction interval on the strain and displacement of the casting billet during the soft reduction process of the casting billet. In addition, the influence of production process parameters such as superheat and casting speed on the quality of the casting billet should also be considered, and the soft reduction process should be optimized from multiple perspectives.It is recommended to consider the influence of process parameters such as reduction amount and reduction interval on the strain and displacement of the casting billet during the soft reduction process of the casting billet. In addition, the influence of production process parameters such as superheat and casting speed on the quality of the casting billet should also be considered, and the soft reduction process should be optimized from multiple perspectives.