Thymoma is not a cancer, but a rare epithelial tumor of unknown etiology, the majority of which are located in the anterior mediastinum, while a few can be located in the neck, pleura, hilum and lung parenchyma. Because of its morphological heterogeneity, thymoma is difficult to define as benign or malignant; moreover, the mediastinal structure is complex, and tumor invasion of different structures may have different effects on patient prognosis. WHO classifies thymic epithelial tumors into thymoma (types A, Bl, B2, B3, AB) or thymic carcinoma (type c) according to the morphology of epithelial tumor cells and the proportion of lymphocytes involved. The clinical presentation of thymoma is mostly asymptomatic, with occasional findings in chest radiographs. Patients may present with chest pain, chest tightness, cough, chest discomfort, weight loss, loss of appetite, exertion, spinal cord compression, and other symptoms. The diagnosis of thymoma needs to be based on medical history and clinical manifestations, the preferred way to diagnose thymoma is CT of the chest, puncture biopsy, surgical diagnosis, and laboratory tests to confirm the diagnosis of pathology. The main treatment for thymoma is surgery. For patients with incompletely resected tumors or unresectable tumors that have progressed locally, or for patients with invasive tumors that have been completely resected, radiotherapy can be used as an adjuvant treatment with certain effect. For benign thymoma, no more treatment is needed after surgery, but regular review is required. The 10-year survival rate of thymoma is 97% for type A, 95% for type AB, 92% for type B1, 81% for type B2, and 62% for type B3. Thymic carcinoma is 29%. In conclusion, although thymomas have inert features and are mild in cytologic presentation, all thymic tumors may have a malignant biological behavior. The best treatment for thymoma should be determined according to the stage. Surgery remains the most important treatment and complete resection is one of the most important prognostic factors for long-term survival, so the tumor should be removed as completely as possible.