Abstract: Noise pollution greatly affects human mental and physical health. Porous sound absorption materials usually perform well in middle and high frequency bands, but improvement still needs in low frequency bands. In this work, hollow sphere foam matrix were prepared with fly-ash hollow sphere and sodium silicate as the raw materials firstly. Subsequently, flexible polyvinyl alcohol-carbon black (PVA-C) composite was introduced into the porous matrix through vacuum impregnation and ordinary heat drying or freeze drying process to obtain PVA-C/hollow sphere foam composites. The results show that the compressive strength of the obtained porous composite is more than 1.65 MPa. The sound absorption performance is improved by 35.2% in the range of 100-1000 Hz, compared with the hollow sphere foam matrix. The noise reduction coefficient reaches 0.523, which is increased by 10.1%. The results of the study provide a basis for the improvement of sound absorption performance and practical application of porous sound absorbing materials.