Inappropriate diet is second only to smoking as a cancer-causing factor, and in developing countries, inappropriate diet and alcohol consumption are responsible for nearly one third of all cancers. Dietary factors are responsible for 25% of all cancers, alcohol consumption causes about 6% of all cancer cases, the absence of obesity reduces cancer by 5%, and obesity increases the risk of breast cancer, endometrial cancer, bowel tumors, and kidney tumors. The reason why tumor is a chronic disease is that the vast majority of cancers are not caused by one time or accidental exposure to carcinogenic substances, but because of long-term poor living habits, living environment and irrational, unscientific dietary hygiene habits lead to, which the correlation between diet and cancer is more significant. A large number of studies have proved that there is a close relationship between diet and the occurrence of cancer, which accounts for 30%-40% in men and 50% in women. Another reason why tumor is a chronic disease is that cancer can be prevented. We can prevent, reduce or delay the occurrence and development of cancer by improving poor living habits, living environment and unreasonable and unscientific dietary hygiene habits. Therefore, we are advised to develop good living and hygienic habits, rationalize nutrition, pay attention to more intake of vegetables, fruits, animal livers and vegetable oils which are rich in cancer inhibitors, and establish good living habits as the best countermeasure to prevent cancer. Only by raising awareness will we be able to “prevent cancer before it occurs”.