Pulmonary effusion is the accumulation of fluid in the pleural cavity. A small amount of fluid may have no obvious symptoms, while a large amount of fluid may show symptoms such as palpitations, dyspnea, coughing and chest pain. There is a small amount of fluid in the pleural cavity, and its filtration and absorption are in a dynamic balance. When the pathogenic factors cause the fluid to be formed too quickly or absorbed too slowly, pleural effusion, or pulmonary effusion, occurs. When the amount of pleural effusion is less than 0.3~0.5L, it may be asymptomatic or insignificant. When there is a large amount of fluid in the pleural cavity, the fluid will compress the lung tissues, leading to a decrease in the effective respiratory volume of the lungs, causing pulmonary insufficiency, dyspnea, chest tightness, palpitations, and in severe cases, respiratory failure. The fluid accumulation irritates the pleura, which can cause chest pain and cough. When pulmonary effusion occurs, it is recommended to consult a doctor in time to clarify the cause of the disease, and if necessary, thoracentesis is needed to extract pleural fluid to alleviate the symptoms, and it is recommended to standardize the treatment under the guidance of a professional doctor.