Thymoma B3 is a low-grade malignant tumor of thymoma. When the tumor enlarges to the extent of compressing different organs, it will lead to corresponding symptoms. 1. When the tumor enlarges to compress the superior vena cava of the patient, it will lead to swelling of the face and upper limbs. 2. When the tumor compresses the trachea of the patient, the patient is prone to have dyspnea, breathlessness and other uncomfortable symptoms. 3. Tumor cells infiltrate the sympathetic nerves of the patients, which may easily trigger Horner’s syndrome, resulting in the patients’ clinical manifestations such as small eye fissures and sunken eyeballs. 4. When thymoma B3 is combined with myasthenia gravis, it is easy to show clinical symptoms such as drooping eyelids, generalized weakness, weakness of respiratory muscles and biting muscles. Because thymoma B3 belongs to low-grade malignant tumor, once diagnosed, it can be treated with surgical resection of the lesion, radiotherapy and other methods under the guidance of doctors, and the prognosis is relatively good.