Embodiments for forming an elastic image in an ultrasound system are disclosed. In one embodiment, an ultrasound data acquisition unit is configured to transmit/receive ultrasound signals to/from a target object to thereby output first ultrasound data. The ultrasound data acquisition unit is configured to transmit/receive ultrasound signals to/from the target object while applying pressure to the target object to thereby output second ultrasound data. A frame image data forming unit is configured to form a first frame image data based on the first ultrasound data. The frame image data forming unit is configured to form a second frame image data based on the second ultrasound data. A processing unit is configured to calculate strain data based on the first and second frame image data. The processing unit is configured to set a reference value based on the strain data. The processing unit is configured to form an elastic image based on the reference value. A control unit is coupled to the ultrasound data acquisition unit, the frame image data forming unit and the processing unit.
