Objective To evaluate the value of two-dimensional (2D) and color Doppler ultrasonography and B-blood flow (B-flow) in quick screening for venous diseases of the lower extremities in late pregnant women. Methods Sixty late pregnant women excluding other-cause blood vessel diseases were recruited during September 2007 to January 2008 and underwent 2D and color Doppler ultrasonography and B-blood flow examinations for diameter and blood flow velocity of the veins in their both lower extremities during prenatal and postnatal periods to record intravenous condition, activities of the venous valve and venous valvular regurgitation in detail. Results Diameters of the veins in beth lower extremities of the late pregnant women widened significantly during prenatal period, as compared to that in postnatal period [(11.5±1.5) mm vs. (8.4±1.0) mm, t =7.14, P <0.01] and their blood flow velocity slowed down significantly in prenatal period than that in postnatal period [(11.5±4.0) cm/s vs. (29.7±6.9) cm/s, t =-15.74, P <0.01]. Spontaneous enhancement phenomenon could be shown in their veins in 57 of 60 (95%) pregnant women by 2D and color Doppler ultrasonography, but could not be shown by 2D and color Doppler uhrasonography in the poplitel veins in 21 pregnant women (35%) or in the small and great saphenous veins in 39 pregnant women (65%), which should be activated by B-flow. Venous valvular regurgitation occurred in the great saphenous veins and the superficial femoral veins in 24 percent of pregnant women during prenatal period, and small venous valve bag thrombus formed in 20 percent of the superficial femoral veins and 10 percent of the great saphenous veins, but disappeared two weeks after delivery, without formation of pulmonary embolism. Conclusion Tow-dimentional and color Doppler ultrasonography and B-blood flow examinations can be used in late pregnant women to quickly screen for venous diseases in their lower extremities.