There are two reasons for the occurrence of pleural effusion in lung cancer: First, cancer cells directly invade the pleura resulting in increased permeability of the pleura, producing a large amount of pleural effusion, which is detected by CT and ultrasound. Clinically, it manifests as heart tiredness, wheezing, chest tightness, and even occurrence of chest pain. Pleural effusion puncture and decompression as well as drug infusion chemotherapy need to be given as early as possible to control the occurrence and development of pleural effusion. Secondly, due to the obstruction of lymphatic circulation by lung cancer, malignant pleural effusion can not be easily detected in the pleural fluid, and pleural biopsy is needed to detect the cancer cells. In conclusion, pleural effusion in lung cancer is mostly a manifestation of advanced stage lung cancer, which requires systemic chemotherapy and local infusion chemotherapy according to the cell classification of squamous carcinoma, adenocarcinoma and small cell carcinoma respectively. Under special circumstances, gene targeting drugs can also be given to control the pleural effusion as soon as possible. If the effect is still unsatisfactory, pleural adhesions can be given to avoid the recurrence of pleural effusion.