PM2.5 can easily penetrate indoor spaces through natural or mechanical ventilation systems, posing a serious threat to human health. Fiber filtration is the predominant technique for indoor particulate matter purification. However, there is an inherent trade-off between achieving high filtration efficiency and maintaining low resistance. Therefore, this study employs a simple and fast adhesive method to fabricate a composite material composed of micro-biochar (BC) and polyurethane (PU) coarse fibers (BC@PU). We developed an electrostatic-assisted air filtration device system that leverages the electrostatic interaction between charged particles and polarized fibers to achieve high-efficiency, low-resistance air filtration. At a face air velocity of 0.4 m/s, the BC-1.5@PU material achieves a remarkable 98.83% removal efficiency for particles in the 0.3–0.5 μm size range, while maintaining a minimal pressure drop of approximately 7 Pa, with the best CQF (comprehensive quality factor) value of 0.408 Pa⁻¹, which was a remarkable 94.06% improvement over the bare PU material. In addition, the simulation results indicate that the micro-biochar significantly enhances the effective electric field range within the composite fibers. It indicates that this composite fiber holds great potential for air purification in ventilation systems.