Abstract: The dynamic responses of bubbles in ultrasonic field include the radial vibration,translation,and their interactions.Based on the radial vibration modal where the secondary radiation of neighboring bubbles was considered, and interaction forces of bubbles,the coupled motion of two bubbles with different size in a plane ultrasonic field was simulated numerically.The results show that the radial vibration of a big bubble has natural properties and its translation velocity is rapid relatively.The behavior and distribution of bubbles were observed experimentally by using high speed photography.It is shown that the big bubbles translate rapidly in bubble clouds and vibrate radially with small-amplitude.On the other hand,the phenomena of attraction and coalescence among bubbles are observed,which may be attributed to the effect of secondary radiation between neighboring bubbles.