The safety of soybean consumption in patients with breast cancer is still controversial. On the one hand it is believed that soybean isoflavones may stimulate the generation of reactive oxygen species and play a certain role in the initiation of breast cancer and the proliferation of cancer cells. On the other hand other studies have shown that after ingesting foods containing soybeans the isoflavone concentration in the serum increased significantly but the isoflavone concentration in the breast tissue changes little. At the same time consumption of isoflavone had no effect on Ki-67 a molecular marker of proliferative activity in breast tissue and the density of mammograms. Isoflavone intake has no adverse effect on the incidence of breast cancer in premenopausal and postmenopausal women but has the effect of preventing breast cancer. At the same time the intake of isoflavones had no effect on the proliferation of breast tissue. For breast cancer survivors after treatment intake of soybean and isoflavones had no significant adverse effects on prognosis and even had a protective effect on postmenopausal breast cancer patients. Therefore according to the epidemiological and clinical evidence obtained at present combined with the 2016 edition of Chinese Dietary Guidelines it is suggested that 10~ 25 g of soybeans or a considerable amount of soybean products should be taken per person per day and women diagnosed with breast cancer should eat soybeans appropriately. This article reviews the role of soybean isoflavones in the prevention of breast cancer whether it has an impact on proliferation whether it will affect breast cancer patients and the mechanism of soybean isoflavones on the pathogenesis and prognosis of breast cancer