<p>The bagasse/polylactic acid (BF/PLA) composite has the advantages of being environmentally friendly and lightweight, but its compatibility was poor. The silane coupling agent-treated BF was blended with PLA to prepare BF/PLA composites using a twin-screw extruder. The properties of the BF/PLA composites were evaluated through capillary rheometry, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), moisture absorption tests, mechanical property, and soil burial degradation behavior analysis. The results showed that when the BF content reached 25%, the tensile strength of composites increased by 66.7%, the yield strength increased by 65.1%, and the elongation at break improved by 35.8%. Rheological testing revealed that fiber agglomeration caused greater flow resistance, resulting in decreased fluidity as the BF content increased. Regarding moisture absorption performance, the treated composite exhibited a significant reduction in water absorption rate. Specifically, when the BF content was 25%, the saturated water absorption rate of BF/PLA composite decreased 89% compared to the untreated BF/PLA composite. DSC analysis showed that the glass transition temperature and melting temperature of BF/PLA composite treated with silane coupling agents increased, and improved thermal stability and structural density of the composites. SEM observations of the composite cross sections revealed that the surfaces of BF/PLA treated with silane coupling agents exhibited pronounced roughness and a uniform coating layer. Pores and cracks were filled, and the fiber surfaces became denser, facilitating stronger interfacial bonding with the matrix. In natural degradation tests, the degradation rate of the untreated BF/PLA was 4.002%, and the degradation rate of treated composite was 0.041% after 6&#xa0;months. The research results are of great significance for expanding the application of sugarcane bagasse.</p>