Far infrared (FIR) is a form of thermal radiation that has beneficial biological effects on human health. As a convenient and non-invasive important type of physiotherapy, FIR has been widely used in clinical fields such as diagnosis and treatment of diseases. The author collected many related works in the literature regarding the clinical application of FIR to elaborate on its molecular mechanism and to summarize its application in diagnosis and clinical treatments of diseases including dysmenorrhea, chronic pain, cough, pressure ulcer, tumor, and diarrhea. This review provides a reference for the disease diagnosis and evaluation of curative effect to promote the clinical application and development of FIR.