The pathogen of mycobacterium intracellulare infection was named by Runyon in 1967. It is a slow-growing, non-photochromogenic bacterium with a short body. It can be isolated from soil, water and animal excrement. Infected birds, mammals and soil rich in bird droppings may be the natural hosts of the bacteria. The bacteria can sometimes be isolated from the secretions of normal people. The pathogenesis is still unclear. The main manifestations are chronic lung infection, lymphadenitis in children, and disseminated infection in immunosuppressed patients (especially AIDS). A large number of acid-fast bacilli can be found in secretions or biopsy tissue smears, and culture examinations can reveal the growth of avian mycobacteria or intracellular mycobacteria. Combination therapy has a better therapeutic effect.