Abstract: In view of the wide frequency noise characteristics of turbofan engine with large bypass ratio at present, traditional single-degree-of-freedom honeycomb sandwich acoustic lining material was optimized to improve its sound absorption performance. Under the premise of keeping the basic form of single-degree-of-freedom honeycomb structure of sound liner unchanged, in order to broaden the sound absorption spectrum and reach two or more characteristic frequencies, carbon nanotube film was compounded at a specific position inside the single-layer honeycomb core. At the same time, in order to improve the sound absorption effect, metal wire mesh and flexible porous materials were introduced between perforated plate and honeycomb core, and they were assembled through a rapid process. The influences of placement position and parameters of the introduced material on the sound absorption performance of the sound absorption composite were also investigated. The experimental results show that the structure with the best sound absorption performance is the introduction of 37 μm hole diameter wire mesh placed behind the porous panel, the placement of 15 mm thick melamine sponge between the porous panel and the honeycomb, and the placement of carbon nanotube film with a porosity of 2% and 4% in the middle of the honeycomb sandwich structure. The sound liner prepared based on this result has excellent sound absorption performance, and shows good sound absorption performance in the range of 800 Hz to 4500 Hz. The peak sound absorption coefficients of the two characteristic frequencies reach 0.98 and 0.99, respectively, and the average sound absorption coefficient reaches 0.89, which is 61.8% higher than that before optimization. At the same time, the half-peak width can fully cover the frequency range of 800 Hz to 4500 Hz tested, which indicates good broadband noise reduction characteristics.