Interfacial modification has been extensively studied in the realm of plant fiber-reinforced bio-composites, with biomimetic polydopamine (PDA) modification garnering significant attention in recent years. This paper presents a novel strategy involving the one-pot co-deposition of PDA cross-linked with polyethyleneimine (PEI) to modify bamboo fibers (BF) for reinforcing polylactic acid (PLA). This approach enhances the interfacial compatibility between BF and PLA through robust linkages in a convenient, green, and non-destructive way. Our findings demonstrate that the PDA cross-linked PEI method is more efficient and controllable compared to the single PDA modification method. Specifically, the flexural strength, tensile strength, and impact strength of PDA/PEI modified composites increased by 26.38 %, 24.11 %, and 49.42 %, respectively. This represents nearly double the enhancement achieved by PDA modification alone, underscoring the efficacy of PDA/PEI cross-linked networks on the BF surface in providing strength, dissipating strain, and promoting interfacial compatibility. Additionally, the modified PLA composites exhibited improved thermal stability and crystallization behavior. This study introduces a unique approach to producing high-performance, eco-friendly bio-composites, thereby facilitating the broader processing and utilization of biomass resources.