With the increasing understanding of cancer as a persistent disease, it is gradually realized that cancer prevention is the most effective weapon in the fight against cancer. Many scientific studies and effective control activities have shown that cancer can be avoided, 1/3 of cancers can be prevented, 1/3 of cancers can be cured if diagnosed early. Reasonable and effective palliative care can improve the quality of life of the remaining 1/3 of cancer patients. Today’s world presents many challenges to our traditional habits, and new perspectives on health have emerged that require ongoing awareness. Individuals, families and even communities are more responsible than ever for helping themselves and others to prevent disease and to improve their lifestyles and environments to promote health. Governments must take appropriate measures to support the activities of individuals, families, and communities. Tumor prevention and control can only be truly preventive if it is incorporated into people’s daily lives and work agendas. The ultimate goal of cancer prevention is to reduce the incidence of cancer and mortality. To achieve this purpose, the following kinds of preventive measures can be adopted: primary prevention, secondary prevention, tertiary prevention and chemoprevention, etc. Primary prevention Class I prevention: The first level of prevention or etiological prevention. Its goal is to prevent the occurrence of cancer. Its tasks include studying various cancer causes and risk factors, taking preventive measures against specific cancer-causing and cancer-promoting factors such as chemical, physical and biological, and disease-causing conditions inside and outside the body, and taking measures to enhance environmental protection, appropriate diet and appropriate sports for a healthy organism, in order to promote physical and mental health. For individuals, this is the 0 period, which is an important “prevention before it happens” period. 1. Avoid smoking Smoking is a well-known cancer-causing factor, which is related to 30% of cancers. Tobacco tar contains many carcinogens and carcinogenic substances, such as 3-4 benzpyrene, polycyclic aromatic hydrocarbons, phenols, nitrosamines, etc. When the smoke of tobacco combustion is inhaled, tar particles are attached to the bronchial mucosa, which can induce carcinogenesis through long-term chronic stimulation. Smoking mainly causes cancer in lung, pharynx, larynx and esophagus, but also increases the risk of tumor in many other areas. 2.Diet Structure The survey of American Diet, Nutrition and Cancer Council (DNC) shows that colon cancer, breast cancer, esophageal cancer, stomach cancer and lung cancer are most likely to be prevented by changing dietary habits. In fact, a proper diet may have a preventive effect on most cancers, especially since there are a variety of cancer-preventive ingredients in plant-based foods that are effective in the prevention of almost all cancers. The 8 dietary guidelines are: Variety of foods, mainly grains. A variety of foods should include grains and potatoes, animal foods, legumes and their products, vegetables and fruits, and pure calorie foods. Eat more vegetables, fruits and potatoes to maintain cardiovascular health, increase resistance to disease, prevent cancer and prevent eye diseases. Eat milk, beans and their products every day. Calcium is generally lacking in our diet, only half of the recommended supply. And dairy foods are high in calcium and are an excellent source of protein, as are beans. Often eat the right amount of fish, poultry, eggs, lean meat, less fatty meat and meat and oil. The amino acid composition of animal protein is comprehensive, with high lysine content; and the unsaturated fatty acids of fish have the effect of lowering blood lipids and preventing thrombosis. Balance diet and physical activity to maintain proper weight. The caloric intake for breakfast, lunch and dinner should be 30%, 40% and 30% respectively. Eat a light and low-salt diet. The average salt intake of our residents is about 15 grams per day, which is more than twice the value recommended by the World Health Organization, so salt intake should be reduced. Drinking alcohol should be moderated. Eat clean, hygienic and non-perishable food. Including the purchase of food that meets health standards, especially green food. 3.Other factors such as occupation, environment, infection, drugs, etc. Exposure to some chemical substances due to occupation and environment can lead to tumors in different parts of the body. For example, lung cancer (asbestos), bladder (aniline dyes), leukemia (benzene). Some infectious diseases are also very closely linked to certain cancers: for example, hepatitis B virus and liver cancer, and human papilloma virus and cervical cancer. In some countries, schistosomal parasitic infections significantly increase the risk of bladder cancer. Exposure to some ionizing rays and large amounts of ultraviolet light, especially from the sun, can also cause certain tumors, especially skin cancer. Commonly used drugs with carcinogenic properties include sex hormones-estrogens and androgens, and the anti-estrogen drug triamcinolone. Widely used estrogens in postmenopausal women are associated with endometrial and breast cancers.