The venous valve undergoes more destruction and malfunction, and the quantity and duration of venous valvular reflux are larger and longer. On the basis of this mechanism, we detected the popliteal vein reflux duration and various influencing factors with duplex ultrasound. The reflux duration longer than 0.5 secand was verified as the evidence of primary venous insufficiency (PVI) in the detection of 40 cases. The detecting method recommended by us is that with standing position, and pneumatic compression 10. 67kPa (80mmHg) applied to calf, the reflux duration through popliteal venous valves is detected by using both pulsed-wave Doppler scanning and color-flow Doppler scanning. With the rates of sensitivity (92%), specificity (100%), and accuracy (94%), this noninvasive, quantitative, and easily handled method showed a very good diagnostic value.