Before puberty, the thymus gland has the function of producing T-lymphocytes, which can participate in the cellular and humoral immunity of the body, and has the function of improving the immunity of the body. After puberty, the thymus gland gradually degenerates, and generally by the age of 14-15, the thymus gland is completely degenerated. If thymus tissue remains in the thymus gland after the age of 14-15, it is called incomplete thymus degeneration, and in adults, the thymus gland is basically completely degenerated. If there is an occupancy in the thymus gland, it should be considered as thymoma or thymic carcinoma. If there is an occupancy larger than 1 cm in the thymus gland, it should be removed by thoracoscopic surgery, and then pathological examination should be done to decide the next step of treatment according to the results of the pathological examination.