The study investigates the effects of different polyhydroxyalkanoates (PHA) contents on the properties of polystyrene (PS) foam composites. The results show that as the mass fraction of PHA increases from 0 to 15%, the density and Vicat softening temperature of the composites increase to 0.54 g/cm³ and 94.10 ℃, respectively, while the porosity and pore size decrease. The mechanical properties (tensile and flexural strength) are enhanced, and the thermal stability is improved. Adding 15% PHA to PS improves the aging resistance and biodegradability of the composites, with a low mass loss rate of only 1.50% and a degradation rate of 12.40% after 90 days. A comprehensive analysis indicates that composites prepared with 15% PHA in PS have potential for application in building walls.