1. An ultrasound system, comprising: an ultrasound probe including a plurality of transducer elements and configured to receive ultrasound echo signals reflected from a target object to acquire ultrasound data; and a processor configured to: form volume data by using the ultrasound data; set a plurality of volume slice regions respectively representing a plurality of rendering ranges of different widths in the volume data on a reference plane image to obtain a plurality of volume slices having different widths; and perform a 3-dimensional ultrasound image rendering according to the plurality of rendering ranges of different widths to form a plurality of 3-dimensional ultrasound images respectively corresponding to the plurality of volume slices having the different widths; and a display configured to display the plurality of 3-dimensional ultrasound images.