Abstract: A segmentation method was studied for the inferior vena cava of fetus in B-mode ultrasound images in this paper. B-mode ultrasound is a technique widely used in clinic for its convenience, but the images of that have the defect of high noise and low contrast. To effectively segment blood vessels in B-mode ultrasound images, in this paper, a segmentation algorithm based on fuzzy sets and region growth algorithm was presented. A fuzzy set algorithm was used to improve the image contrast in advance, and then the adaptive region growth algorithm was presented based on gradient to segment the image. In this paper, taking the doctor's manual segmentation result as the gold standard, the threshold segmentation and level set algorithm were compared. The experiments show that, the accuracy and stability of this method are higher than threshold segmentation and level segmentation.