Herein, the 3D characterization of internal defects in medium carbon steel with different soft reduction (SR) parameters is investigated, as regards its spatial morphology and size distribution using X‐ray computed tomography. The size of defects and their shape complexity increase from the equiaxed toward the center of the ingot, and the total number of defects is larger at the equiaxed region, which exhibits the aggregation and growth of small spherical pores into the large defects from equiaxed toward the center region. The two types of shrinkage defects, including island and net shrinkage, are identified. With the minimum reduction amount of 2 and 4 mm, the number and size of defects along with the carbon macrosegregation in the equiaxed region and center of the ingot are less as compared to the high reduction amount of 6 mm and without SR technology. The size of gas pores with sphericity >0.6 is <70 um with different reduction amounts and exceeds up to 150 um without SR. Therefore, minimum reduction amounts can easily regulate the internal defects in medium carbon steel.