Lung cancer can be judged whether there is pleural metastasis through clinical manifestations, pleural fluid examination, thoracoscopy and imaging examination. 1. Clinical manifestations: when lung cancer invades the pleura, patients may have persistent severe chest pain. 2. Pleural fluid examination: lung cancer cells may invade the pleura of dirty layer and cause pleural effusion, at this time, pleural fluid can be extracted and smeared to find cancer cells. 3. Thoracoscopy: Thoracoscopy can comprehensively explore the chest cavity and biopsy the pleura, lungs and lymph nodes of hilar mediastinum to find lesions. When other examinations fail to make diagnosis, thoracoscopy can be chosen to take pleural tissue biopsy to find cancerous tissues. 4. Imaging examination: such as chest X-ray, chest CT, when the cancer cells invade the pleura, there will be corresponding imaging causing pleural effusion. Lung cancer usually metastasizes to the pleura through direct diffusion. Lung cancer patients diagnosed through pathology should formulate diagnosis and treatment strategies under the guidance of professional physicians as early as possible, and take active treatment.