The causes of thrombus include endothelial injury, blood flow disorders, abnormal blood components, other triggering factors, etc. Muscle pain in the affected limbs, muscle spasms, bruising and edema of the skin of the affected limbs, chest pain and other symptoms can occur. 1. Vascular endothelial injury: the most important and common cause of thrombus formation, mostly seen in infective endocarditis, rheumatic endocarditis, severe atherosclerotic plaque ulceration. 2. Disturbance of blood flow: mainly refers to the slowing down of blood flow and the production of eddies in blood flow, etc. The activated coagulation factors and prothrombin reach the concentration required for coagulation locally, which is conducive to the formation of thrombus. 3. Abnormalities of blood components: usually refers to the increase of platelets and coagulation factors in the blood, the decrease of activity of fibrinolytic system and so on, leading to hypercoagulable state of the blood, which is mostly seen in hereditary and acquired hypercoagulable state. 4. Other triggers: for example, prolonged bed rest after surgery, restricted venous return function, resulting in stagnation of blood flow, oral contraceptive pills and hormones, long-term smoking and alcohol abuse, pregnancy, etc. Thrombosis can lead to narrowing and occlusion of the blood vessel, resulting in ischemia of the organs or impaired venous return, etc. If the thrombus is dislodged and embolized to other locations, it can also lead to acute thromboembolism. The common symptoms of thrombosis are related to the site of thrombosis, such as deep vein thrombosis of the lower limbs can lead to muscle pain, muscle spasm, skin bruising and edema of the affected limbs, etc., such as plaque rupture of the coronary artery leading to acute thrombosis, which can lead to acute infarction, severe chest pain, dyspnea, profuse sweating, and a sense of impending death. It is recommended that patients with thrombosis consult a doctor in time to identify the cause and standardize the treatment under the guidance of the doctor.