In this study, we developed an ecofriendly and high-toughness hemp-derived micro/nano fibrous preform that can be utilized as a filler layer of biodegradable natural fiber–reinforced plastic. The alkali treatment of hemp raw material promoted the microfibrillation of hemp fiber bundles, maximizing the surface area and imparting a pore structure when manufacturing the preform. Hemp-derived cellulose nanocrystals were extracted and utilized as a nanobinder for the fibrous preform, which induced surface coating of hemp-derived microfibers and strong bonding between fibers, exhibiting excellent structural stability and mechanical strength. In addition, the nanoscale roughness and dispersive surface energy induced by CNCs improved interfacial compatibility with the PBS matrix, enabling stronger fiber–matrix bonding. The fiber-reinforced plastic, which was a composite of hemp-derived micro/nano hybrid preform and biodegradable poly(butylene succinate), exhibited a reinforcing effect that improved tensile strength by 171 %, Young’s modulus by 746 %, and toughness by 132 % compared to the conventional poly(butylene succinate). This hemp-derived multiscale hybrid fibrous preform could not only replace conventional synthetic fiber–reinforced plastic materials but also have various potential applications in biodegradable products.