Polycystic ovary syndrome (PCOS) is a common clinical condition in gynecological endocrinology, and the etiology of PCOS is still unclear. Obesity (especially central obesity), hyperandrogenism and insulin resistance are three mutually reinforcing factors. Among them, insulin resistance seriously affects the long-term health outcomes of PCOS patients. Menstrual disorders, anovulatory infertility and obesity have an important relationship, which in the long run will lead to serious consequences: abnormal lipid metabolism, abnormal glucose tolerance and/or type 2 diabetes, hypertension, etc. Weight loss, especially abdominal fat reduction, can reduce circulating insulin levels, which will not only restore ovulation and promote fertility, but also prevent the development of serious metabolic diseases, and its therapeutic effect is even better than drugs. Lifestyle modification can reduce weight and insulin resistance, which is an important treatment for PCOS. With appropriate diet and exercise, a 5% weight loss may restore menstrual cycles and increase ovulation rates, making it the first choice for obese infertile PCOS patients. The National Institutes of Health (NIH) guidelines for the long-term treatment of overweight and obesity are: (1) Adopt a proper diet and good eating habits. (2) Adhere to long-term effective physical activity. (3) Behavior therapy, reduce stress, maintain a good psychological state. (4) Behavioral therapy, diet and exercise therapy combined treatment. (5) Support from doctors, family, spouse and obese patients is important for weight reduction. (6) Quit smoking and reduce alcohol consumption. (7) Avoid excessive dieting and excessive weight loss in a short period of time. (8) Drug weight reduction is not used as the main method of weight reduction. (9) Surgical weight reduction is not used as the main method of weight reduction. (10) Different weight loss programs should be designed for different obese individuals. (11) For obese patients with successful weight reduction, long-term follow-up observation should be carried out, and patients should be encouraged to avoid weight rebound. Lifestyle modification should be the basis of pharmacological treatment for obese and overweight patients with PCOS. Exercise and diet control to achieve weight loss can restore health and fertility, save time and money, and reduce the incidence of metabolic syndrome.