Abstract: Based on the microstructure features of xonotlite-aerogel composite insulation material, a three dimensional unit cell model was developed for the coupled heat transfer of gas and solid in the material. The effective thermal conductivities of xonotlite-type calcium silicate, aerogel and xonotlite-aerogel composite insulation material were compared by model calculation. The results show that the density of xonotlite-type calcium silicate has great influence on the effective thermal conductivity of xonotlite-aerogel composite insulation material, but the density of aerogel has little influence. The effective thermal conductivity of xonotlite-aerogel composite insulation material is apparently lower than those of xonotlite-type calcium silicate and aerogel at an elevated temperature.