A large amount of unilateral fluid in the chest cavity may be the inflammatory stage of the disease, malignant tumor, chest wall trauma, etc., and the cause of the disease should be identified by timely consultation. 1. Inflammatory stage of the disease: suffering from pneumonia, tuberculosis and so on. These patients have low fever, chest pain, dry cough and other symptoms for a long time. With the continuous development of the disease, the chest cavity will also continue to increase, which will lead to the situation of unilateral large amount of fluid in the chest cavity. 2. Malignant tumor: patients suffering from metastatic tumors such as lung cancer, pleural tumor, breast cancer, etc., can have unilateral large amount of fluid accumulation in the chest cavity in the middle and late stages of cancer, and with the aggravation of the condition, bilateral fluid accumulation can occur. 3. Chest wall trauma: after trauma, the blood vessel of pleural cavity is damaged, and the permeability of blood vessel wall changes, pleural effusion will occur, which will result in unilateral large amount of fluid accumulation in chest cavity. This symptom alone is not enough to diagnose the disease, and may be caused by other factors. It is recommended that the patient consult a doctor in time to clarify the cause of the disease and give targeted treatment.