Abstract: This study focuses on the organic modification of fly ash (FA) using silane coupling agent KH570, titanate coupling agent CS201, and stearic acid (SA) to enhance its compatibility with polymers and incorporate it into an intumescent fireproof coating system, thereby improving the coating's fire resistance and thermal insulation properties. The structure and composition of the FA composite flame-retardant fillers were characterized using FT-IR and SEM. The effects of different organic modification methods on the flame-retardant performance and thermal insulation capabilities of the intumescent coatings were systematically investigated. Experimental results revealed that under conditions of an external flame temperature of 1200±50℃ and a combustion duration of 60 minutes, the SFA coating (SA-modified FA coating) exhibited superior performance compared to KFA (KH570-modified FA) and CFA (CS201-modified FA) coatings. Specifically, the SFA coating demonstrated a lower backside temperature (147.1℃), a reduced equivalent thermal conductivity (0.023 W/(m·℃)), and a higher residual weight (17.83%) as indicated by TG-DTG analysis. Additionally, the SFA coating formed a denser expanded char layer, highlighting its excellent thermal insulation and anti-ablation properties. Furthermore, all three modified coatings exhibited bond strengths exceeding 0.20 MPa, meeting the requirements for practical engineering applications. This study offers new insights and approaches for the utilization of industrial solid waste as an eco-friendly flame-retardant filler.