1. An ultrasound system, comprising: an ultrasound acquisition unit including an ultrasound probe for transmitting ultrasound signals to a target object and receiving echo signals, the ultrasound acquisition unit being configured to form a plurality of ultrasound data based on the echo signals; and a processing unit coupled to the ultrasound acquisition unit and configured to form first to N th ultrasound images by using the plurality of ultrasound data, wherein N is a positive integer greater than 1, the processing unit being further configured to estimate a motion degree of an ultrasound probe and process the N th ultrasound image based on the motion degree.