Abstract: The present study aims to develop an eco-friendly flame retardant, enhancing the flame retardancy of polyvinyl chloride (PVC) composites through microencapsulation modification technology. Starch (S) was employed as the encapsulating material to modify magnesium hydroxide (MH) via hydrogen bonding, successfully preparing starch-microencapsulated flame retardant (S-MH). Subsequently, S-MH was compounded with graphene oxide (GO) and applied to PVC composites to improve their comprehensive performance. Multiple characterization methods were utilized to analyze the thermal stability, flame retardancy, smoke suppression performance, and mechanical properties of PVC/S-MH@GO composites.Experimental results indicated that compared with pure PVC, the char residue rate of PVC/S-MH@GO composites at 800°C significantly increased by 7.1%. Furthermore, the limiting oxygen index (LOI) value increased from 23.4% to 28.7%, demonstrating remarkable improvement in flame retardancy. In terms of smoke suppression, the maximum specific optical density of PVC/S-MH@GO decreased by 15.494% compared to pure PVC, showing excellent smoke suppression effect. Mechanical property tests revealed that the tensile strength and elongation at break of PVC/S-MH@GO reached 10.6 MPa and 461.3%, respectively, which were significantly higher than those of PVC/MH (11 MPa, 234.3%) and PVC/GO (10.2 MPa, 206.7%).Combined with SEM results before and after combustion, the S-MH@GO flame retardant was uniformly dispersed in the PVC matrix, forming a dense char layer structure, thereby effectively enhancing the thermal stability, flame retardancy, and smoke suppression performance of the composites. This study not only provides a new solution for flame retardant modification of PVC materials but also offers theoretical basis and practical guidance for the design and development of eco-friendly flame retardants.