Lung cancer is an important cause of pulmonary embolism. Not only lung cancer, but also other malignant tumors can cause pulmonary embolism. Because lung cancer tends to secrete procoagulant substances, which tend to stimulate platelet aggregation in blood circulation, thus activating the coagulation system. The activated coagulation factors will form thrombus, and the thrombus in the blood circulation can reach the pulmonary artery through the blood circulation, thus leading to the occurrence of pulmonary embolism. Once pulmonary embolism occurs, the patient may manifest cough, blood in sputum and difficulty in breathing in light cases, and in serious cases, it may lead to cardiogenic shock and sudden death of the patient. Therefore, lung cancer can completely lead to pulmonary embolism. Patients with lung cancer should pay attention to screening for pulmonary embolism, and a CT angiography of the pulmonary arteries can confirm the diagnosis. Of course, a venous ultrasound of both lower extremities is needed before that to detect any deep vein thrombosis.