There are provided embodiments for performing a frame average process based on a change of a frame rate are disclosed. In one embodiment, an ultrasound system comprises: an ultrasound data acquisition unit configured to sequentially acquire ultrasound data corresponding to a living body and a processing unit configured to sequentially form a plurality of ultrasound images based on the ultrasound data, estimate a frame average coefficient corresponding to a change of a frame rate based on an ith (i is a positive integer) ultrasound image and an ith frame average image, and perform a frame average process between the ith frame average image and an (i+1)th ultrasound image based on the frame average coefficient to form an (i+1)th frame average image.
