A silane coupling agent (named KH-550) was used to modify composite intumescent flame retardant containing tea saponin (CTS-IFR), which was applied in flame retardant coatings. The preparation conditions of the silane coupling agent modified tea saponin flame retardant(SMTS-IFR)were investigated. The structure of SMTS-IFR was characterized by FT-IR and SEM, the thermal decomposition properties were performed by simultaneous thermal analyzer, and the flame retardant and combustion performance of coatings containing SMTS-IFR(SMTS-IPRC) were also measured by Cone calorimeter. The results showed that the suitable modification reaction conditions were at the temperature of 80 ℃, the reaction time of 4 h, and the addition of 2.5% silane coupling agent in tea saponin intumescent flame retardant. It showed that the reaction between silane coupling agent and flame retardant system occured, and the flame retardant was cladded and dispersed uniformly. SMTS-IFR had good thermal stability and higher carbon residue at high temperature compared with that of CTS-IFR. Cone calorimeter test showed that coating sample containing SMTS-IFR had a good flame retardant with a heat release rate for an average of 62.29 kW/m2,a total heat release of 52.66 kJ/m2，a mean effective heat of combustion of 11.31 kJ/kg, and an average mass loss rate of 0.046 91 g/s in the combustion process, which was significantly improved compared with the coating containing unmodified flame retardant.