Porous foam materials have good sound absorption properties. In this paper, a series of polystyrene (PS) composite foams were prepared by supercritical CO2 foaming. Insight of large-scale and low-cost production of foams, we presented a feasible extrudated foaming process of PS composites with lignin by using supercritical CO2 as the physical blowing agent. The composite foams showed elongated cell morphology; meanwhile the compressive strength and the sound transmission loss(STL) value were greatly increased. These composite foams presented remarkable high performance of the sound transmission loss(STL), The STL values of composite foams with 10 wt% lignin composites were about 15 dB higher than that of pure PS foam. The density can be as low as 0.068g/cm3, and there is a broader prospect in industrial applications. Considering the feasible, large-scale and low-cost production process, these foams are expected to apply in sound insulation.