It is not nonsense to say that the occurrence and development of cancer is closely related to psychological factors. From the real life, we often hear that someone was found out to have cancer soon after suffering from mental stimulation due to excessive tension, fear, anxiety or depression. A colleague of mine went to the hospital for a medical checkup and was found to be suffering from stomach cancer because he was depressed and drowned his sorrows with alcohol. Another good friend lost money in business and was called by his creditors. He often felt nervous, fearful, frightened and anxious, unable to eat or sleep, and lost tens of pounds in more than three months. One of the enlightenment of these phenomena in real life is that excessive tension and depressed emotion can be one of the causes of cancer. Some people may say that maybe it is just a coincidence, but scientists’ study that excessive stress and depression can cause cancer is not just a coincidence, as the following research results from some scientists in Japan, the United States and Australia at the end of the 20th century need to be understood about the relationship between mental factors and cancer: Japanese researchers found in the comparative observation of test rats that those who suffered from mental stimulation once every other day In a comparative observation of mice in Japan, researchers found that mice that were subjected to mental stimulation once every other day were more likely to develop lung cancer than mice in the comparison group that were not subjected to similar stimulation. Scientists in the United States and Australia conducted a comparative psychological study of thousands of cancer patients and healthy individuals and confirmed that the risk of colon and rectal cancer was tens of times greater in people with high levels of mental stress than in people with low levels of mental stress. In his book “The Doctrine of Mental Stress and Oppression”, the famous Canadian physician Hans Selys pointed out that “it has become common knowledge in cancer immunology that about 80% of cancers in humans are caused by carcinogenic factors in the environment.” At present, the reasons for the increased incidence of cancer caused by emotional tension and mental stress are still unclear, but there are two main points of view: 1. It may be that the adverse mental factors may cause a significant decrease in the body’s immunity, which makes it easy for mutated cells to break through the immune barrier and form a fixed value and add value, which may develop into cancer. 2. Mental factors may cause changes in the flow of endocrine hormones or promote the generation of free radicals, which may also induce cancer to occur. Therefore, it is important for the human body to maintain a happy mood and cheerful lifestyle. People should try to arrange and adjust their lives, reduce stress, try to get away from the negative effects of bad emotions such as sad face, anger and excessive sadness, and live happily with a relaxed and cheerful mood. When in a bad mental state, they should actively adjust and try to transfer it, such as chatting, taking a walk or participating in some cultural and sports activities that can help relieve emotions, and try to be optimistic and open-minded, have a harmonious family, live a stable life and maintain a calm and stable mental and psychological environment in order to reduce the incidence of cancer and reduce the harm of cancer.