Abstract: The formation and spatial distribution of ultrasonic cavitation in the cylindrical reactor of 20 kHz are studied. The distribution of the acoustic energy density in the cylindrical sound field is obtained by using Bessel function, and the finite element method is used for simulation analysis. By combining the acoustic measurement method and the sono-chemi luminescent (SCL) method, the theoretical analysis results are verified in the power ultrasonic experiment of 20 kHz. The results show that the ultrasonic cavitation effect appears in the end region of the horn when the cavity radius is R=50 mm, the resonant liquid level of 20 kHz is H=90mm and the current of Power Amplifier is <40 mA, in the case of 40 mA ≤ the current of Power Amplifier ≤ 80 mA, the cavitation effect is significantly enhanced; that the spatial distribution of the cavitation effect is consistent with the distribution of sound pressure in the field, the acoustic modes affect the cavitation effect to form the distribution characteristics of the far-field cavitation effect, and when the current of Power Amplifier is >80 mA, due to nonlinear factors, the cavitation effect is distributed in a cylindrical tail shape under the action of the acoustic flow at the resonant liquid level, and a tile-like distribution is formed at the boundary of the bottom wall; and that for the non-resonant liquid level of 75 mm, with the increase of power, the ultrasonic cavitation effect appears only in the end region of the horn and presents the local cavitation distribution characteristics.