A 33-year-old young patient was recently admitted to the hospital due to the finding of “chest tumor” on physical examination. The enhanced CT scan of the chest clearly showed a solid tumor of nearly 10 cm in size in the right upper mediastinum, with a thin strip of compression of the left and right lateral unnamed veins. Considering the impact of surgery on the patient, the majority of the department suggested a right-sided thoracoscopic additional incision approach to remove the tumor. Intraoperatively, the tumor was found to be closely related to the pericardium, the bilateral innominate veins and the superior vena cava. The tumor was gradually detached and the left sessile vein involved by the tumor was excised, and this mediastinal tumor of nearly 10 cm was completely removed in 9.5 hours. At the end of the operation, it was already early the next morning, and the surgical team remembered that they had already crossed the “waxing and waning” in the intense operation. Intraoperative rapid pathology failed to clarify the specific origin of the tumor. The specific pathology results are yet to be further clarified. It is worth mentioning that a tumor of such a large size has partially blocked the main venous access from the head and neck and upper limbs bilaterally, and the left unnamed vein has been invaded by the tumor, but the patient had no special symptoms and discomfort. On the other hand, it also highlights the importance and necessity of health examination.