Most of the obstruction of superior vena cava reflux is caused by malignant tumors, such as lung cancer, primary mediastinal tumors, lymphoma and metastatic tumors, etc. Chronic mediastinitis and primary superior vena cava thrombosis can also be caused. The clinical examination methods are as follows. Chest X-ray can show upper mediastinal mass, enlarged mediastinal and paratracheal lymph nodes, and pleural fluid, and CT examination is more suitable for those who have no typical findings on chest X-ray. Endoscopic or dissecting lung biopsy or lymph node biopsy, or cytological examination are used to clarify the etiology. Chest CT or MRI can help to clarify the cause of superior vena cava obstruction. Ultrasound imaging can visualize the site of obstruction and the morphology of the lesion. Radionuclide venography can show venous obstruction. Enhanced CT of the chest is important for the diagnosis of the disease, not only to understand its etiology, but also to observe the site and extent of the obstruction and the collateral circulation, which is widely used in clinical practice. If the cause is suspected to be malignant, a biopsy is also needed to obtain a pathological diagnosis. Biopsy methods include fiberoptic bronchoscopy, CT-guided puncture biopsy or mediastinoscopy, etc.