Necrotizing enterocolitis (NEC) is a common critical gastrointestinal disease in neonates. Severe cases have a poor prognosis and may be fatal. Early and accurate diagnosis is crucial for improving outcomes. Traditional abdominal X-ray has low sensitivity. As a noninvasive, radiation-free real-time imaging technique, abdominal ultrasound can assess intestinal wall structure, peristalsis, and perfusion at an early stage and has outstanding value for early diagnosis. Typical ultrasound findings include intestinal wall thickening or thinning, abnormal blood perfusion, pneumatosis intestinalis, portal venous gas, pneumoperitoneum, and complex ascites. Ultrasound outperforms X-ray in identifying these signs, and it is particularly useful when X-ray findings are inconclusive or when dynamic monitoring is required. It can be considered one of the preferred imaging modalities for NEC.