Silicone modified epoxy resins were prepared via polycondensation of polyphenylmethoxy(PPMS) and epoxy resin (E-20). The flame retardant properties of cured silicone modified epoxy resins were inverstigated by limiting oxygen index (LOI), UL-94 testing and thermogravimetric analysis (TGA).When the mass ratio of E-20 to PPMS was 7:3, the cured modified epoxy resin exhibits the optimal effect. The LOI value was 21.5%, higher than those of unmodified epoxy resins systems by 4%.The burning rate was reduced from 36.23mm/min to 26.60mm/min. The TGA date indicated that the thermal oxidative degradation process of the cured modified epoxy resin is composed of two steps.The 5% weight loss temperature of degradation was 134.7℃, higher than the unmodified epoxy resins by 28.3℃. The residue weight for the cured modified epoxy resin at the temperature of 750℃ was 25.79%,compared to the original date of 0.21% at 750℃ .The chemical structure of char for the resin at the end of LOI test was analyzed by Fourier transform infrared. Based on above results, the flame retardant mechanism was discussed.