Tumor is a cytogenetic disease in which normal cells in the organism, under the long-term action of different initiating and promoting factors, produce neoplastic organisms formed by proliferation and abnormal differentiation. Once the neoplasm is formed, it does not stop proliferation due to the elimination of the cause. It is not regulated by the physiology of the body, and instead of normal growth, it destroys normal tissues and organs. According to the effect of tumor on human body, it can be divided into benign and malignant. Most of the malignant tumors are called cancer, which can metastasize to other parts of the body, making treatment difficult and life-threatening. Research published by the World Health Organization says that cancer cases and deaths are disturbingly increasing worldwide, with nearly half of all new cancer cases occurring in Asia, most of them in China, which has the highest number of new cancer cases. China leads the world in new cases and deaths of four malignancies: liver, esophagus, stomach and lung. The most common malignant tumors in China are lung cancer, colorectal cancer, stomach cancer, liver cancer and breast cancer in order in urban areas; and lung cancer, stomach pain, esophageal cancer, liver cancer and breast cancer in order in rural areas. Lung cancer, gastrointestinal tumor and liver cancer are the most common tumors in men, while breast cancer, lung cancer, gastrointestinal tumor and liver cancer are the most common tumors in women. Research shows that with the development of medical research and advancement of medical technology, 1/3 of cancers can be prevented, 1/3 can be cured and 1/3 can be treated to improve symptoms. The three levels of cancer prevention include: Ⅰ prevention is etiological prevention, eliminating or reducing the factors that may cause cancer, preventing the occurrence of malignant tumors and reducing the incidence rate; Ⅱ prevention is how to detect and treat cancer at its early stage once it occurs, improving the survival rate and reducing the mortality rate; Ⅲ prevention is rehabilitation after diagnosis and treatment, improving the quality of survival, reducing pain and prolonging life. Grade I prevention of tumor, also known as etiological prevention, refers to the research to clarify the causes and carcinogenic factors, and for the general population, to take active preventive measures against the clearer carcinogenic factors, to eliminate or block the causes, to minimize the risk factors of cancer, to improve the body’s ability to prevent cancer, to promote health, to prevent the occurrence of cancer before it happens. Its tasks include studying the causes and risk factors of various cancers, taking preventive measures against specific cancer-causing and cancer-promoting factors such as chemical, physical and biological, as well as internal and external disease-causing conditions. At present, many risk factors of malignant tumors have been clarified, including environment, living habits, diet, nutrition, genetics, viral infections and other factors interacting with each other to cause them. (2) Quit smoking and drinking alcohol; (3) Eat a reasonable diet and pay attention to nutritional balance; (4) Strengthen physical exercise; (5) Immunization; (6) Avoid occupational exposure to prevent occupation-related tumors; (7) Receive health education, etc., so as to reduce the occurrence of tumors by reducing the exposure to these risk factors. For example, viral hepatitis B is one of the important risk factors for liver cancer. 10% – 15% of the population in China carries hepatitis B virus surface hang original, through the popularization of hepatitis B vaccination, it can effectively prevent and stop the hepatitis epidemic and mother-to-child transmission, thus reducing the incidence of liver cancer. Research on human papillomavirus, which is associated with cervical cancer, and EBV, which is associated with nasopharyngeal cancer, has also made great progress. Grade II prevention of tumor, also known as preclinical prevention and pathogenetic prevention, refers to the screening of precancerous lesions or early tumors for specific high-risk (high-risk) populations so as to provide early detection, early diagnosis, early treatment, active treatment of precancerous lesions, interrupting the occurrence of cancer, preventing the development of incipient disease, and preventing the disease from developing at the beginning, thus playing a multiplier effect with half the effort. It plays an important role in reducing the incidence of tumors, improving the cure rate and reducing the mortality rate. The main means to achieve the level II prevention is the screening work for early detection of potential or hidden diseases and early detection of cancer in the asymptomatic natural population. In order to improve the effectiveness of screening work, it is often carried out in a selective population, generally targeting high-risk groups of certain tumors for selective screening, which can stop or slow down the development of the disease, detect and diagnose precancerous lesions, and significantly improve the prognosis of detected tumors. To improve the screening benefit, the exact high-risk group should be established, including age, gender, family disease status, exposure to risk factors, and having relevant symptomatic changes are all factors for selection. Simple, effective, economical and easy-to-use screening methods with high specificity and sensitivity for certain tumors should be applied to screen high-risk groups. For example, the detection of human papillomavirus infection and cervical exfoliative cell smear for cervical cancer have a good cost-benefit ratio, and the decline in mortality from cervical cancer in China is largely attributed to the implementation of screening measures. Although breast cancer is still the first malignant tumor in women, organized breast screening, including simple, economical and convenient breast self-examination, breast ultrasound and mammography, has improved the detection rate of breast cancer, and the detection rate of early breast cancer has increased significantly, improving the cure rate and survival quality, and the mortality rate of breast cancer ranks only the fifth in the history rate of malignant tumors in women. Screening for rectal cancer by fecal occult blood, anal finger examination and colonoscopy, and removal of colorectal polyps to prevent the development of colorectal cancer. Serum prostate-specific antigen testing and prostate ultrasound to detect prostate cancer, etc. Grade III prevention of tumor, also known as clinical stage prevention or rehabilitative prevention, refers to a series of measures for patients with existing tumor to provide reasonable treatment through existing medical technology and means to eliminate tumor, carry out rehabilitation after diagnosis and treatment, promote rehabilitation, try to restore function, reduce its complications, prevent deterioration, prevent recurrence and metastasis, prevent disability, improve survival quality, increase survival and rehabilitation rate In addition, we can also reduce the pain caused by tumor and prolong life. The main means is to adopt multidisciplinary comprehensive diagnosis and treatment, and correctly choose the reasonable or even the best treatment plan. With the continuous improvement of modern diagnosis and treatment level and deeper research on the pathogenesis, comprehensive treatment and individualized treatment should be actively advocated. Palliative care and hospice care should be provided to patients with advanced disease. We should care for cancer patients from physical and psychological aspects, such as setting up associations, patient associations, clubs, anti-cancer associations, etc., and regular follow-up and communication between medical staff and patients. As mentioned above, there are more and more preventive measures for cancer, and the aspects involved are more and more extensive. With the development of medicine, cancer prevention has accumulated a lot of experience both theoretically and practically, and with effective measures, cancer will be better prevented. Care for life, scientific cancer prevention, and better life.