Synthetic microbial communities are artificial systems composed of multiple microorganisms with well-defined genetic backgrounds. They are characterized by low complexity, high controllability, and strong stability, thus suitable for industrial production, disease management, and environmental remediation. This review summarizes the design principles and construction methods of synthetic microbial communities, and highlights their application in polyhydroxyalkanoate (PHA) biosynthesis. Constructing a synthetic microbial community represents a core research direction of synthetic ecology and an emerging frontier of synthetic biology. It requires strategies to design and control microbial interactions, spatial organization, robustness maintenance, and biocontainment to obtain an efficient, stable, and controllable synthetic microbial community. In recent years, synthetic microbial communities have been widely used to synthesize high-value chemicals such as drugs, biofuels, and biomaterials. As an ideal substitute for oil-based plastics, PHA has received much attention. Enhancing the capacity and broadening the range of carbon source utilization for PHA producers have become the research priority in the application of synthetic microbial communities for PHA biosynthesis, with the aim to reduce PHA production cost.