Abstract: How to achieve the broadband sound absorption of the micro-perforated panel (MPP) sound absorber is one of the research hotspots in designing low-frequency absorber. To solve this problem, a design of irregular back cavity structure is proposed and applied to the single-layer and double-layer micro-perforated panel absorber, and their sound absorption performances are studied in this paper. The impedance relationship of each part of the microperforated panel absorber is obtained by the equivalent circuit model (ECM), and their impedance and sound absorption coefficient are calculated by theory. The theoretical, simulated and experimental results show that without increasing the thickness of the structure, the sound absorption bandwidth of MPP can be broadened by unequal volume segmentation of the back cavity through the inner variable cross-section partition, and the structure is relatively simple. This study provides a design idea for broadband low-frequency sound absorption and its application of MPP absorbers.