Lung cancer stage IV belongs to advanced stage, and the appearance of malignant pleural effusion can be treated by controlling primary disease, chest drainage and symptomatic treatment. 1. Controlling primary disease: the presence of pleural effusion in stage IV lung cancer indicates that the lung tumor has invaded the pleura, and chemotherapy and targeted drug therapy can be given to control the growth of the tumor according to the assessment of the patient’s physical status, so as to reduce the production of pleural effusion. 2. Thoracic drainage: if malignant pleural effusion occurs in stage IV lung cancer, the growth rate is often very fast, causing symptoms such as chest tightness, chest pain, dyspnea, etc., and it is necessary to relieve the compression and alleviate the condition through thoracic drainage. 3. Symptomatic treatment: patients with stage IV lung cancer may have hypoproteinemia, which will aggravate the formation of pleural effusion, so intravenous albumin supplementation can be used to assist treatment. After malignant pleural effusion occurs in stage IV lung cancer, it is recommended to consult doctor in time and choose appropriate treatment according to doctor’s instruction to avoid delaying the condition.