Objective To design a computer aided method in HIFU treatment system to monitor the size,shape and location of HIFU lesion automatically.Methods According to ultrasound image's characters of high noise,low resolution and weak edge,a double zero level set,double speed approach was proposed to extract the contour of organ and lesion area.The serial "lice" contours were used to reconstruct three dimension(3D) HIFU lesion area in the sample.Results Experiments show that level set contour extraction method based 3D reconstruction is helpful in monitoring the size,shape and location in the organ.Conclusion This method has the feasibility to be introduced as an auxiliary technique monitoring HIFU lesion area automatically.