Pericardial effusion from lung cancer is caused by the invasion of lung cancer cells into the pericardium causing cancerous exudate. The malignant tumor cells of the lung infiltrate the pericardium of the heart, causing a constant leakage of water from the blood in the pericardial capillaries into the pericardial cavity. When the volume of fluid accumulation reaches a certain volume, it will lead to restriction of heart beat, just like putting the heart into a container filled with water, and the patient can experience ischemia and hypoxia of organ tissues due to a sharp decrease of heart output. The clinical manifestations are chest tightness, shortness of breath, dyspnea, and cyanosis of the lips and mouth, which in severe cases can lead to heart failure and cause death of the patient. The treatment means, including two major aspects of symptom alleviation and elimination of the cause of the disease. When a large amount of pericardial fluid causes chest tightness and shortness of breath, pericardial puncture and drainage can be performed to drain the fluid from the pericardium and relieve the patient’s discomfort, which is the symptom treatment. The real cure is to remove the tumor cells through chemotherapy, targeted therapy and other anti-tumor treatments to eliminate the cause of the disease, and then the pericardial effusion will be absorbed and disappear on its own.