<p>Bio-based flame retardants have gained significant attention due to their environmental friendliness and sustainability, becoming a research hotspot in the field of flame retardants. Calcium gluconate (CG) was modified by phenylphosphinic acid (PPA) to form phosphorus-containing calcium gluconate (CP), which is then used as both the carbon and gas source. Phytic acid (PA) is used as the acid source, PA-Na as the phosphorus and carbon source, and acrylic emulsion as the film-forming substance to prepare a flame-retardant coating for polypropylene (PP). The results show that the coating containing 30 mass% of flame retardant in a thickness of 250&#xa0;μm imparts UL-94 V-0 classification and an LOI value of 20.6% to PP. The formulation significantly increases the char yield of PP, reduces the release of flammable volatile products, and decreases peak heat release rate (PHRR), total heat release (THR), smoke production rate (SPR), and fire growth rate index (FIGRA) by 67.3%, 63.5%, 53%, and 68%, respectively. As regard to the flame-retardant mechanism, phosphorus PO· and HPO· radicals will be released from the flame retardant agent in the coating (including CP, PA, and PA-Na) during combustion, and they scavenge H· and HO· radicals to terminate the chain reaction, thereby suppress flame propagation.Additionally, the formation of dense char layers containing CaCO₃ and/or CaO and stable metal/phosphorus crystalline compounds further enhances the flame-retardant effect. Moreover, the prepared flame-retardant coating demonstrates excellent adhesion and flexibility, achieving an adhesion grade of 5B. These findings provide new insights and technical support for developing high-performance flame-retardant materials, offering significant application potential.</p>