There are several kinds of examinations for pleural effusion as follows: 1.Take chest plain film can find pleural effusion, but cannot find pleural disease, and then do lung CT; 2.Chest ultrasound: besides suggesting the amount of pleural effusion, there is also the role of localization, which can be used to extract pleural effusion for laboratory test to understand the cause; 3.Biochemical, routine, tumor examination, and pathogenic examination can clarify the cause; 4.Pleural biopsy: it is better to do pleural biopsy when there is a large amount of pleural effusion, but the positive rate is low, so it is basically not done now; 5.Pleural biopsy is not done now. 4, pleural biopsy: pleural biopsy is more effective when a large amount of pleural effusion is done, but the positive rate is relatively low, so it is basically not done now; 5, patients with unexplained pleural effusion need to do thoracoscopy to clarify the diagnosis.