Obesity is a risk factor for type 2 diabetes, cardiovascular diseases, and various cancers. The prevention and treatment of obesity have become the focus of public health. Omega-3 polyunsaturated fatty acids (n-3 PUFA) are polyunsaturated fatty acids extracted from deep-sea fish. The anti-inflammatory and triglyceride-lowering properties of n-3 PUFA are well known, but its role in the treatment of obesity is still controversial. In animal models, n-3 PUFA can effectively reduce fat. However, in humans, existing studies have shown that n-3 PUFA may not contribute to weight loss, but may slow down weight gain. N-3 PUFA can improve the metabolic changes associated with obesity by regulating intestinal flora, regulating lipid metabolism, suppressing appetite, alleviating adipose tissue inflammation and altering epigenetic mechanisms, thus playing an important role in the prevention and treatment of obesity and the related metabolic diseases.