Phases of tissue harmonic motions, induced by the ultrasound radiation force, over a distance can be detected by pulse echo ultrasound and Kalman filter. However, large background motions due to cardiovascular motion distort the weak harmonic vibration. The background motion can be modeled by the Wiener process or random-walk process. The harmonic motion and the background motion are represented by a fourth-order differential equation and four state variables. Based on this model, the Kalman filter estimates phase shifts of shear wave over a short distance in a tissue region from large background motions. The study shows that the estimates are valid when the velocity and acceleration of background motion are less than 3 m/s and 3 m/s/s, respectively.