Whether lymph node enlargement of lung cancer is metastasis depends mainly on whether the enlarged lymph node is ipsilateral or contralateral. If the lymph nodes of lung cancer are enlarged contralaterally, it should be considered as lymph node metastasis, and further examination should be given to chest enhancement CT and PET-CT. Enhancement CT can detect enlarged lymph nodes, which have shown the possibility of lung cancer metastasis, while PET-CT can understand whether the patient with enlarged lymph nodes has increased glucose metabolism, which also indicates lung cancer lymph node metastasis. Mediastinoscopy and puncture of the hilar lymph nodes can directly understand whether the lymph nodes are metastases of cancerous tissues, but the operation is invasive and risky, so patient consent and preoperative assessment of whether the patient can undergo this test are required. In conclusion, whether the lymph node enlargement of lung cancer is metastasis or not should be further understood based on enhanced CT and PET-CT examination of the chest.