The causes of low fever in lung cancer patients include tumor fever, bacterial and fungal infections, side effects of drugs and so on. 1. The progression of lung cancer patient’s condition leads to the appearance of tumor fever, and the specific mechanism of this tumor fever is not clear at present. Tumor fever is usually manifested as low fever, which often occurs in the afternoon, and it can be relieved by itself or the body temperature can be returned to normal after treatment, and it is usually common in patients with late-stage lung cancer. 2. Lung cancer disease itself or due to radiotherapy and other treatments related to lung cancer may cause the immunity of human body to decline and secondary infectious fever, such as bacterial infection, fungal infection, viral infection and so on. 3. Lung cancer patients use some targeted drugs or immunity drugs, which may also cause the side effect of low fever. When lung cancer patients have low fever, it is recommended to consult doctor for further clarification of the cause of the disease, and carry out treatment according to the cause of the disease.