An ultrasound system for estimating tissue deformation in ultrasound elasticity imaging includes a controller configured to deliver a plurality of tracking pulses and to obtain a plurality of data sets for a region of interest from an ultrasound transducer array; a harmonic data analyzing circuit configured to receive the plurality of data sets and to extract one or more harmonic data sets including harmonic signals from the plurality of image data sets; and a displacement estimator circuit configured to estimate tissue deformation in the region of interest responsive to the one or more harmonic data sets.