Leg thrombosis refers to lower extremity blood clots, a bout of pain refers to paroxysmal pain, and constant pain refers to persistent pain. Lower extremity thrombosis can be divided into lower extremity arterial thrombosis and lower extremity venous thrombosis, different types of symptoms are also different, mostly persistent pain. 1. Lower extremity arterial thrombosis: it is usually detached from the heart and flows to the lower extremities through the body circulation, blocking the arteries, causing local ischemia and hypoxia, and even necrosis. In the early stage, it can be manifested as sudden coldness and pallor of the lower limbs, which may be accompanied by slight pain. With the prolongation of the blockage time, the necrosis of the tissues increases and the pain gradually worsens, which is manifested as persistent severe pain, bruising of the skin, and gangrene can appear in serious cases. 2. Lower extremity venous thrombosis: It is formed because of abnormal coagulation function, damage of blood vessel wall, slow blood flow and other reasons, which leads to abnormal coagulation of blood in the lower extremity. It can be divided into superficial vein thrombosis and deep vein thrombosis. The common symptoms of superficial vein thrombosis of the lower limbs are pain and redness along the direction of venous flow, and localized pressure pain. Deep vein thrombosis of the lower limbs, in the acute stage, is characterized by swelling of the lower limbs, which may be accompanied by rest pain, that is, persistent pain in the state of limb rest, not relieved by rest, and aggravated by pain at night. With the recanalization or partial recanalization of the deep veins after entering the subacute phase, the swelling and distension can be reduced. When symptoms such as lower limb pain and swelling occur, it is recommended to consult a doctor in time to clarify the cause of the disease, and the condition should not be judged by pain.