The invention discloses a graphite-polystyrene foamed plastic extruded plate for heat insulation. The graphite-polystyrene foamed plastic extruded plate for heat insulation comprises the following raw materials in parts by mass: 70-80 parts of PS polystyrene, 5-13 parts of expanded graphite, 1-5 parts of talcum powder, 6-10 parts of a flame retardant, 0.2-1.5 parts of carbon black and 3-4 parts of a CO2 foamer. A preparation method for the extruded plate comprises the following steps: independently warehousing the raw materials according to components; automatically controlling system loading, mixing and stirring; carrying out high-temperature first-order plasticization through a screw with a length of 15m and an average temperature of more than 180 DEG C; carrying out second-order plasticization through a screw with a high temperature of 210 DEG C and a length of 10m; injecting the CO2 foamer under a high pressure and foaming by a mould; conveying the material into a shaping platform and carrying out extrusion moulding; carrying out primary cooling moulding on the graphite extruded plate; cutting corners; secondarily processing (galling, grooving and knurling); transversally cutting; secondarily cooling; packaging and warehousing. The extruded plate disclosed by the invention is a black plate, and has the characteristics of being good in fire resistance, high in heat insulation capacity, lower in cost for achieving the same effect, convenient to construct, and good in system integrality.