Ultrasonic welding is one of the welding process to apply the ultrasonic vibration to the overlapping metal plates. It has been known that normal and shear force on the contact surface of two metals play an important role in the welding process, and the corresponding frictional energy dissipation is related to the strength of weld. Specifically, welding condition may vary according to the normal and tangential force, and phase difference of two forces. Thus, to understand the mechanism of the ultrasonic welding, the contact condition during the process should be analyzed. In this paper, we estimate the contact and shear force according to different contact status when the displacement control vibration on the two contacted materials is applied, by using numerical approach. In addition, the frictional energy dissipation is calculated according to the phase difference of vertical and horizontal vibration, dimensions, and material properties of weld metals.