Human milk (HM) has been associated with a lower risk of necrotizing enterocolitis (NEC). However, the association of precise HM proportion with the outcome of NEC remains unclear. A total of 77 cases and 154 matched controls were included in this study. The samples were divided into three groups based on the HM proportion of the total enteral intake before NEC onset: ≥70% (HHM), <70% (LHM), and 0% (NHM). The study cohort did not show a significant association between different HM proportions and NEC risk. The adjusted odds ratio (OR) for the highest versus the lowest intake was 0.599. In the prognosis of NEC, different HM proportions significantly affected weight gain, the timing of NEC onset, diagnosis time, hospitalization cost, and the severity of NEC (p < 0.05). Our findings support the beneficial effects of HM on reducing NEC in preterm infants, particularly when a greater proportion of HM of the total enteral intake is included in their feeding. Additionally, the study indicates that preterm infants fed with lower proportions of HM of the total enteral feeding are more prone to experiencing severe cases of NEC.