Some solidification defects such as macrosegregation and porosity will occur during the solidification of GCr15SiMn steel ingots. In order to develop a more reasonable die casting process, the GCr15SiMn ingot of 1 kg was smelted in vacuum induction furnace. And the similarity between laboratory and industrial production was studied from the perspective of the die casting process and the macrostructure of ingot. The correlation between the carbon segregation and porosity of GCr15SiMn ingot was studied by OPA and SEM. The results showed that the segregation of carbon was the most serious and related to porosity. The relationship between segregation degree (S) of carbon and compactness degree (P) can be expressed as SC=0.92P－0.89. The basic law embodied in this formula was applicable to industrial ingots. According to the statistical results of SEM and OPA, the corresponding relationship between the equivalent diameter of the porosity and the quantitative characterization value (compactness degree P) was established. The result showed that the segregation degree of carbon increased with the increase of the equivalent diameter of porosity. The Scheil model was used to analyze and discuss in principle, and it was found that the segregation degree of carbon was positively correlated with the shrinkage of molten steel.