Abstract: The radial vibration characteristics of an annular ultrasonic concentrator is presented and studied.Based on the electro-mechanical analogy and by introducing the area ratio coefficient,the radial equivalent circuit and the frequency equation of the concentrator are derived.And the radial displacement amplitude magnification coefficient of the concentrator is obtained.By numerical calculating,the relationship between the radial displacement amplitude magnification coefficient,the resonance frequency at the first and second order vibration modal and the radius ratio of the concentrator are investigated.Also,the relationship between the radial displacement amplitude magnification coefficient and resonance frequency of the concentrator and the length,the angle and the number of the silts is analyzed.It is illustrated that a maximum of displacement amplitude magnification coefficient of the concentrator appears with the increase of the radius ratio,and the amplitude magnification coefficient increases as the slit length,the angle and the number of the silts increases,while the radial resonance frequency of the concentrator decrease as the length,the angle and the number of the silts increased.The theoretical resonance frequencies are in good agreement with that of the FEM simulations and measurement.