<p>Thin and small low-frequency sound absorption structures have been an important research topic. In this paper, we combined the features of nanofiber membrane and micro-perforated structure to prepare a two-sized micro-perforated nanofiber membrane and explored its acoustic performance and mechanism as a small-size acoustic structure in the field of low-frequency noise reduction. The low-cost, non-toxic, and high-spinning speed polyvinyl butyral (PVB) was used as the raw material, which was developed into the nanofiber membrane by electrospinning. On this basis, PVB two-sized micro-perforated nanofiber membranes were fabricated through mechanical drilling. The effects of partition, perforation parameters, thickness, and cavity depth on acoustic performance were investigated theoretically and experimentally. The results demonstrated that the two-sized micro-perforated nanofiber membrane had excellent acoustic performance both in the low and medium frequencies. The addition of the partition not only broadened the sound absorption bandwidth but also shifted the resonance absorption peak to low frequency. Furthermore, by reasonably selecting and optimizing the structural parameters such as perforation parameters, fiber membrane thickness, and cavity depth, the range of effective sound-absorbing frequency bands could be adjusted to better meet the demand for noise reduction. Two-sized micro-perforated nanofiber membrane’s effective acoustic absorption bandwidth could reach 2,136&#xa0;Hz in the 100–2,500&#xa0;Hz range, which accounted for about 89% of the whole bandwidth. PVB two-sized micro-perforated nanofiber membrane with its superior sound absorption performance and thin fiber structure body become the ideal choice for flexible and lightweight acoustic materials in the field of acoustic noise reduction.</p> Graphical Abstract <p></p>