Abstract: Microperforated sound absorbers are widely used in the construction, the automobile, the aerospace and other fields. In this paper, the p-u sound intensity probe is used to study the effect of the cavity volume of the double-layer micro-perforated sound absorber on the sound absorption performance. By comparing with the sound absorption coefficient measured in the impendance tube, it is verified that the p-u sound intensity probe can be used to measure the sound absorption coefficient of the double layer micro-perforated sound absorber effectively, and it can also be used under the real size of the test piecee, while the traditional impedance test method can not. The measurement results by using the p-u sound intensity probe show that the cavity resonance can improve the sound absorption performance of the double-layer micro-perforated sound absorber, and the reasonable design based on the cavity resonance frequency is a new idea for the optimal design of the micro-perforated sound absorber.