Polyamide 66 (PA66) fabric has attracted significant attention due to its excellent overall performance. However, its flammability and melt droplet defects severely restricted its wide application. In this work, we successfully developed a bio-based multifunctional intumescent flame retardant (MIFR) coating for PA66 fabric via the interactions between quaternary chitosan (QC), tannins (TA), 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and 4-Formylphenylboronic acid (4-FB). The results indicated that the coated polyamide 66 (PA66) fabric (P-PA66@TA@QC) achieved a limiting oxygen index (LOI) of 30.1 % and no molten droplets generated during the combustion. Additionally, the peak heat release rate (pHRR) and total heat release rate (THR) of P-PA66@TA@QC were reduced by 50.3 % and 55.7 %, while the total smoke production (TSP) was decreased by 80 % compared to the control sample, exhibiting a lower fire risk and excellent smoke suppression performances. Furthermore, P-PA66@TA@QC exhibited good hydrophilicity, high UV protection factor (UPF >
180), and high inhibition rate against E. coli (>
99.9 %) and S. aureus (>
99.9 %), indicating outstanding UV resistance and excellent antibacterial properties. This study successfully developed a bio-based multifunctional flame retardant coating, providing significant guidance for preparing eco-friendly and multifunctional PA66 fabrics.