Adults with persistent low fever for 1 month usually need to consider whether it is caused by infectious or non-infectious factors. Infectious factors are mainly caused by infections such as bacteria, viruses, atypical pathogens and fungi, while non-infectious factors should be considered whether they are caused by cancer, hematological tumors, hyperthyroidism and immune diseases. Persistent low fever in adults is generally defined as axillary body temperature between 37.3-38°C. There are many causes of low fever, and several systemic diseases may cause low fever, so persistent low fever in adults for 1 month must be taken seriously, and it is recommended to be hospitalized in the infection department or respiratory department of the hospital for further systematic examination, treatment and diagnosis to be clear.