Breast cancer is a common malignant tumor among women, and about 1.2 million women worldwide suffer from breast cancer and 500,000 die from it every year. The incidence rate of breast cancer in China is low, but there is a significant increasing trend in recent years. Epidemiology of breast cancer (I) Geographical distribution Globally, North America and Northern Europe are the high incidence areas of breast cancer, Southern Europe and South America are medium incidence areas, and most Asian and African countries are low incidence areas. The incidence and mortality rates in large coastal cities in China are higher than those in inland areas. In terms of urban-rural distribution, the incidence rate is higher in urban than in rural areas. The regional distribution of breast cancer mortality is basically the same as the incidence rate, and the high mortality areas are still Europe and North America. The incidence of breast cancer has been on the rise in recent years, and the incidence of breast cancer has increased in all age groups. The mortality rate was essentially unchanged and stable. The incidence of breast cancer is negatively correlated with the intensity of sunlight. From the regional view of breast cancer incidence in the world, its low incidence area is near the equator, and its incidence rate increases with the increase of the earth’s latitude, and the incidence rate of breast cancer in the northern half of the United States is 1.5-2.0 times of that in the southern half, and the incidence rate of breast cancer in China is also higher in the northern region than in the south. (B) Population distribution Breast cancer is more common in women and less common in men, and only about 1 in men. Among adult women in the same age group, unmarried women have a higher incidence than married women. In terms of age group, the incidence rate increases with age and decreases slightly at the age of 55 years for women. The incidence rate of breast cancer in China increases steeply with age after 25 years of age, and then becomes more stable until around menopause, and can be slightly reduced after menopause. （The incidence rate of breast cancer has some racial differences, the incidence rate of white people in the United States is higher than that of black people, the incidence rate of Han Chinese is higher than that of ethnic minorities in China, and the mortality rate is lower among Mongolians and Tibetans. (iv) Immigration relationship Women from low incidence countries who migrate to high incidence countries have higher incidence rates than their birthplace and lower incidence rates than their place of migration. The incidence rate of Chinese women in San Francisco was four times higher than that of Shanghai women and lower than that of local women; while the incidence rate of the second generation was close to that of the locals. (E) Epidemiological trends of breast cancer incidence The incidence of new breast cancer worldwide was 541,000 people/year in 1975, and the incidence rate exceeded 8,000,000 people/year in 2000, according to the trend of breast cancer incidence to younger people, breast cancer will become a common disease. The current epidemiological survey of breast cancer has shown this trend, and it is necessary to pay attention to the preventive research of this disease when it is in the low incidence stage.