1. An ultrasound system, comprising: an ultrasound data acquisitor configured to form transmit signals having different phases between a n th frame and a (n+1) th frame, the ultrasound data acquisitor being further configured to transmit and receive ultrasound signals to and from a target object based on the transmit signals to output ultrasound data; and a processor in communication with the ultrasound data acquisitor, the processor being configured to form motion data corresponding to motion of the target object based on a phase difference between the ultrasound data corresponding to the n th frame and the ultrasound data corresponding to the (n+1) th frame, the processor being further configured to form a motion image corresponding to the motion of the target object based on the motion data.