Cooling uniformity has a great influence on slab solidification. To study its effect on the internal reduction efficiency, a thermo-mechanical coupling slab solidification model was studied and an internal reduction efficiency calculation model was established. Numerical simulation was performed with ProCAST software and verified by a pin shooting test. The results showed that under uniform cooling, when the reduction amount was more than 3 mm, the internal reduction efficiency was 38–41%, and under non-uniform cooling, the internal reduction efficiency for the 1/4 width and 1/8 width of the slab was 21–28%, while that for the 1/2 width was 45–47%. The soft reduction process parameters was optimized accordingly. Industrial trials showed that an increase in the reduction amount could decrease the central segregation for the 1/4 width of the slab, and the maximum central carbon segregation index was reduced from 1.29 to 1.18.
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