Abstract: The silane coupling agent and alkaline solution were used for surface treatment on the bagasse fiber (BF), and the influence of surface treatment methods on the mechanical property of BF/PLA composite were investigated. The morphology of the impact section of BF/PLA composite was observed by SEM. The results show that surface treatment on BF can improve the interface compatibility between BF and PLA matrix and enhance the mechanical strength of BF/PLA composite to some extent. Among the three surface treatments investigated, the silane coupling agent treatment after being treated by alkaline solution on BF performs the best effect on improving the mechanical property of BF/PLA composite, and the mechanical strength of BF/PLA composite can keep 85.42% tensile strength and 59.74% impact strength of neat PLA after treated by alkaline solution combined with silane coupling agent even the mass fraction of BF reaches 40%. Moreover, the surface of BF turns rough, specific surface area grows larger, length-diameter ratio increases and the interfacial adhesion enhances after being treated by alkaline, which result in the effective improvement of the machanical property.