Whether or not a small amount of fluid in the right lung is serious depends on the cause of the accumulation. When a small amount of pleural effusion occurs in the right side of the chest, the patient mostly needs to try to clarify its cause. If not actively and effectively treated, the amount of pleural effusion may gradually increase and aggravate the patient’s clinical symptoms, with symptoms such as chest tightness, shortness of breath and fever. Some patients may also form pleural adhesion and hypertrophy, resulting in corresponding complications and sequelae. If the pleural effusion is caused by lung infection, the disease is relatively serious, and the pleural effusion can be effectively relieved and absorbed through effective anti-infection treatment. For patients caused by lung cancer, their condition is even more serious, and most of the patients are in the terminal stage of the disease, with a significantly shorter survival period. If it is caused by pulmonary embolism, its condition is critical, and if the patient is not treated with effective anticoagulation or thrombolysis, the patient’s life is in danger. Therefore, when a small amount of pleural effusion occurs, we should pay attention to it and actively diagnose and treat it.