The phenolic resin foam was prepared by using hollow phenolic resin microspher which was made by microcapsule. And under the protection of Ar, the microcapsules were carbonized at 1000 degrees C and graphited at 2000 degrees C, then the foam was got. Herein the porosity and the effect of heat treatment temperature on carbon foam were investigated. And the results show that the porosity increasement can reduce the thermal conduction of material, and the low thermal conduction foam is obtained by using this method. However, for the materials with approximative porosity, the thermal conduction is decreased by reducing aperture of material. Finally, the foam material is obtained with density of 0.50g/cm(3), thermal conduction of 1.007W/m.K and compressive strength of 8.82MPa.