Abstract: Graphite oxide (GO) was introduced into phenol resin (PF) by in situ intercalative polymerization. The obtained phenol (PG) was coated on the surface of expandable polystyrene (EPS) as a flame retardant, which was processed to thermal insulation board. The flame retardant, thermal, and mechanical properties were tested. It showed that the flame retardancy of EPS increased significantly by the coating of PG, however, the thermal and mechanical properties were declined when the GP or GO contents were too high.