Using the degradable polymers polylactic acid (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) as raw materials, a PLA/PBAT mixed polymer matrix was produced by shear melt extrusion in a mass ratio of 75:25. The silane coupling agent KH-550, the modified bamboo powder (KBP), was selected as the reinforcing phase. The compression molding process was used to produce the bamboo powder composites (PLA/PBAT/KBP), and the physicochemical properties of the materials were characterized and tested. The results of differential scanning calorimetry (DSC) and polarized optical microscopy (POM) showed that PBAT and KBP synergistically promoted the rapid formation and growth of PLA crystallites through heterogeneous nucleation effects and increased the crystallinity of the composite material. The results of the mechanical tests showed that the addition of a certain amount of KBP did not significantly weaken the mechanical properties of the polymer matrix but improved the tensile and flexural modulus of the composite material. Therefore, the addition of bamboo powder can reduce the use of biomass polyester, effectively reduce production costs, and make a beneficial attempt to replace plastic with bamboo while achieving comprehensive utilization of resources.