Composite bio–based multifunctional air filtration is a great challenge and development trend for personal protection. This work was inspired by nature mutualism to produce bio–based and essential oil loaded nanofibrous membrane with multiple functions of high–performance, antibacterial, and mosquito–repellent. The cinnamaldehyde (CMA) and poly(hexamethylene biguanide) (PHMB) were introduced into the cellulose acetate (CA) polymer system to achieve functionalization, and then the CA/CMA/PHMB ultrafine bimodal nanofibrous membrane was prepared through one–step electrospinning. Compared to eugenol, the CMA contributed to the refinement of fiber and minimized the reduction of mechanical properties, thermal stability, and hydrophobicity. On the other hand, the PHMB enhanced jet splitting and synergistically improved antibacterial ability with CMA. The filtration efficiency for PM_0.3, the pressure drop, and the quality factor were 99.78%, 59.5 Pa, and 0.1028 Pa⁻¹, respectively. The bacteriostatic rates against Escherichia coli and Staphylococcus aureus, and the mosquito–repellent rate were 99.65%, 99.99%, and 92.7%, respectively. Lastly, the batch preparation of this solution was explored, which contributed to commercialization. This work provides a novel and simple approach to efficiently fabricate multifunctional high–performance air filter, which will promote the development of bio–based and sustainable air filter.