There are four causes of leukemia: first, viral factors, the pathogenic role of RNA viruses in animals such as mice, cats, chickens and cows has been confirmed, and most of the leukemias caused by these viruses are of the T-cell type. Second, chemical factors, some chemical substances have a leukemia-causing effect, exposure to benzene and its derivatives of the population, the incidence of leukemia is higher than the general population. There are also reports of leukemia induced by nitrosamines, povidone and its derivatives, chloramphenicol and so on. Certain anti-tumor cytotoxic drugs, such as nitrogen mustard, cyclophosphamide, etc. have leukemia-inducing effects. Third, radiation factors, there is evidence that a variety of ionizing radiation can cause human leukemia, leukemia depends on the dose of radiation absorbed by the human body, the whole body or part of the torso by a medium dose or large dose of radiation can induce leukemia. Whether small doses of radiation can cause leukemia is still uncertain, frequent exposure to radioactive substances, the incidence of leukemia increased significantly, high-dose radiation diagnosis and treatment can also increase the incidence of leukemia. Fourth, genetic factors, there are chromosomal aberrations in the population leukemia incidence rate is higher than that of normal people.