Abstract: Conventional wet-spun polyacrylonitrile (PAN) fibers suffer from difficult solvent recovery and environmental pollution, so greener alternative processes are required. In this work, an ionic-liquid-based melt spinning process was developed to prepare PAN fibers at low cost using an environmentally benign, non-polluting ionic-liquid solvent. Phytic acid/urea-modified bamboo charcoal powder (BC) was incorporated as a bio-based carbon filler to enhance the mechanical properties of the PAN fibers. Phosphorus–nitrogen polar functional groups were grafted onto the BC surface by chemical modification to strengthen its interfacial interactions with PAN molecular chains. The results showed that, when the loading of modified bamboo charcoal powder (m-BC) was 3wt%, the tensile strength and modulus of the composite fibers increased by 33.09% and 22.04%, respectively, compared with neat PAN, and the fibers exhibited enhanced thermal stability with a higher char yield and a lower decomposition rate. X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR) analyses confirmed that the polar functional groups of m-BC significantly promoted the interfacial bonding between PAN and the filler. This ionic-liquid-assisted melt spinning approach provides a new strategy for constructing high-performance and environmentally friendly PAN composite fibers.