The epoxy-polysiloxane copolymer （ES） was synthesized by condensation reaction of hydroxy-terminated polydimethylsiloxane （HTPDMS） and bisphenol A epoxy resin （CYD-128），and then blended with phenolic resin to modify and obtain polysiloxane modified epoxy/phenolic blend （ES/PF）.Thermal properties of ES/PF blend and the chemical structure and composition of pyrolysis residues at different temperatures were investigated by thermogravimetry-differential scanning calorimetry （TGA-DSC）， fourier transform infrared spectroscopy （FTIR）， scanning electron microscopy with energy dispersive spectrometer （SEM-EDS），and X-ray photoelectron spectroscopy （XPS）.The results show that， compared with pure phenolic resin， the residual yield of ES/PF blend increases by 438% at 800 ℃ in air atmosphere， and the maximum heat release rate decreases from 21.98 W/g to 14.93 W/g. However， under N₂ atmosphere， the residual yield decreases slightly by 14.3%.In addition， the hybrid structure rich in Si-O_x in the pyrolysis condensed phase of ES/PF blend system within 430-600 ℃ plays a key role in the stable formation of carbon layer， effectively delaying and inhibiting the further degradation of resin， and thus improving the carbon residue rate.When the temperature exceeds 430 ℃， the existing form of silicon element in the residue changes significantly，from SiO₂ （accounting for more than 80%） at 430 ℃ to hydrated silica （SiO₂·nH₂O） at 600 ℃. These results fully indicate that the silicon element can significantly improve the carbon residue and thermal stability of phenolic resin under thermal oxygen condition， but its influence is suppressed to a certain extent under N₂ conditions， which may be attributed to the oxygen absorption mechanism of siloxane groups during pyrolysis process. In addition， the structure and composition of pyrolysis residues of ES/PF blend system have a positive effect on improving the thermal residual strength and ablation resistance of the material.