Lower extremity venous ultrasound requires first selecting a high frequency vascular ultrasound probe and then modulating the vascular ultrasound examination mode. Patients need to be examined in the supine position, standing position or sitting position, during the examination, patients need to fully expose both lower limbs, it is generally recommended to wear loose-fitting underwear, and outer pants need to be completely removed. The operator sweeps from top to bottom and from inside to outside in a sequential manner. The operator should be gentle and should not press hard to prevent the lumen from being compressed to prevent visualization of the venous lumen. Especially when deep vein thrombosis is detected, the operator should not press hard to avoid pulmonary embolism caused by dislodgment of thrombus, which may endanger the patient’s life. Secondly, to observe the function of venous valves, it is necessary to do the Watt’s test, first let the patient practice deep inhalation and stomach bulging, some patients with poor cooperation will affect the effect of the examination, or let the patient stand in a standing position to better observe the function of the venous valves, the presence or absence of venous regurgitation and varicose veins.