Thymectomy is the main treatment for thymoma and other thymic diseases. But the incidence of non-therapeutic thymectomy is high due to the difficulty in the differential diagnosis of anterior mediastinum lesions. Formerly, it was believed that the thymus gradually degraded and lost function with aging, and the preservation of the thymus was not valued. Recent studies have found that the removal of the thymus at all ages has adverse effects on overall health and leads to a significant increase in the risk of autoimmune diseases, malignancy, and all-cause mortality. Therefore, unnecessary thymectomy should be avoided. This article reviews the influence of thymectomy, including the changes of immunological indexes and clinical prognosis, and further discusses the current situation and avoidance methods of non-therapeutic thymectomy.