The symptoms of venous thrombosis depend on the location of the venous thrombosis, and the common sites of venous thrombosis are lower extremity veins, upper extremity veins, and intra-abdominal veins. The most common site of thrombosis is lower extremity vein thrombosis, which includes superficial and deep vein thrombosis. The formation of thrombosis in the superficial veins often produces manifestations of thrombophlebitis, such as high skin temperature, red skin, swelling of the tissue around the diseased vein, pain in the diseased vessel, especially when the pain is further aggravated by activity, and the pain is unbearable; some patients also have mild fever. If the thrombus develops further, the size of the thrombus increases, leading to deep vein thrombosis. Deep vein thrombosis occurs in the lower extremities, and most patients experience swelling and edema of the lower extremities, in addition to pain, erythema, fever, superficial venous dilatation, pain in the lower legs during foot dorsiflexion, and cyanosis of the swollen lower extremities. If the deep vein thrombosis dislodges into the pulmonary artery, it will cause pulmonary embolism, and the patient will have coughing, dyspnea, panic, elevated blood pressure, which is life-threatening, and sudden fall or even sudden death will occur if the treatment is not timely. If the veins of lower limbs are not treated timely, post-deep vein thrombosis syndrome will occur, with repeated swelling and painful discomfort of lower limbs, dark skin color, hard skin and loss of elasticity, skin eczema and ulcers, etc. Symptoms of upper extremity venous thrombosis include painful swelling and sunken swelling of upper extremities. Visceral vein thrombosis manifests as no sensation when mild to abdominal pain when severe, etc. Mesenteric vein thrombosis may lead to intestinal necrosis and manifestations of peritonitis. In summary, the symptoms of venous thrombosis vary depending on the site of onset, but all may manifest pain, and thrombosis in the limbs manifests as swelling and pain.