The invention discloses a fireproof insulation board of an outer wall.The fireproof insulation board is prepared from 31-34 parts of cement, 32-39 parts of fly ash, 4-7 parts of quartz powder, 2-5 parts of paper pulp, 9-14 parts of inorganic fibers, 4-9 parts of lime, 1-3 parts of a water reducing agent, 1-3 parts of a composite activity activator, 35-85 parts of fly ash, 11-42 parts of vitrified microbeads, 12-35 parts of acrylic acid emulsion, 4-9 parts of a halogen-free phosphorus series, 2-11 parts of glass fibers, 1-6 parts of a defoaming agent and 1-4 parts of a dispersing agent.The outer side of a main structure is wrapped by the fireproof insulation board of the outer wall, therefore, the main structure can be protected, and the life of a building can be prolonged; hot bridges of a building structure can be effectively decreased, the effective space of the building is increased, the wall surface water condensation phenomenon caused by cold bridges and the hot bridges can be eliminated, and the living comfort degree is improved; the physical performances such as sound insulation and heat insulation of other building materials are not influenced; the fireproof insulation board is more beneficial for volatilization of harmful substances in an outer wall heat insulation material.