The invention discloses a flame-retardant hard polyurethane foam material and a preparation method thereof, and belongs to the technical field of polyurethane materials, wherein the flame-retardant hard polyurethane foam material comprises a component A and a component B, the component A comprises, by mass, 100 parts of polymethylene polyphenyl polyisocyanate, the component B comprises, by mass, 90-100 parts of sucrose polyether polyol, 10-25 parts of a foaming agent, 1-10 parts of a chain extender, 2-6 parts of a foam stabilizer, 2-10 parts of a cross-linking agent, 0.5-8 parts of a catalyst,8-15 parts of a flame retardant and 8-30 parts of glass fibers, and the diameter of the glass fiber is 0.2-0.4 mm. According to the invention, the flame-retardant hard polyurethane foam material hasadvantages of simple preparation process, high strength, light weight, low heat conductivity, good dimensional stability and self-extinguishing after leaving fire, greatly reduces the risk of fire disasters, and creates good conditions for personnel escape and fire extinguishment rescue at the same time.