If the symptoms and signs of lower extremity DVT are not obvious, the diagnosis can be assisted by imaging tests, including ultrasonography, CT venography, magnetic resonance venography, venography and laboratory tests. 1. Ultrasonography: with high sensitivity, high accuracy and low cost, it is widely carried out in clinic and is the first choice of auxiliary examination for the diagnosis of lower extremity DVT. 2. CT venography: this method is highly accurate and can accurately determine the anatomical relationship between the lesion and the surrounding tissues. 3. Magnetic resonance venography: it can accurately show iliac, femoral and popliteal vein thrombosis and the surrounding soft tissues, but there is a big limitation in the imaging of calf deep vein thrombosis. The examination is free of ionizing radiation, suitable for pregnant women, and does not require contrast medium. 4. Phlebography: With high accuracy, it can effectively determine the presence or absence of thrombus, the location of the lesion, the extent of involvement, the time of formation and collateral circulation, and can accurately assess the condition, which is the gold standard for the diagnosis of DVT in the lower limbs. 5. Laboratory tests: D-dimer is often checked during physical examination. When there is thrombosis, this item often has obvious elevation. Lower extremity deep vein thrombosis is a common disease in clinic, once the thrombus is dislodged, there is a risk of causing serious complications, when abnormalities are found, you should go to the hospital in time, and be diagnosed and treated under the guidance of a professional doctor, so as not to be negligent, so as not to delay the condition.