1. An ultrasound system, comprising: an ultrasound data acquisition unit configured to transmit an ultrasound signal to a target object including vessels, receive an ultrasound echo signal reflected from the target object and form ultrasound data corresponding to the target object; a volume data forming unit configured to form volume data based on the ultrasound data; and a processor configured to form a 3-dimensional ultrasound image based on the volume data, set a plurality of slices on the 3-dimensional ultrasound image and perform segmentation of the vessels based on a degree of registration between the respective vessels on the adjacent slices.