The invention discloses a water-proof, high-strength, weather resistance, flame-retardant and environment-friendly thermal insulation board and a preparation method thereof. The thermal insulation board is prepared from the following raw materials in parts by weight: 30-40 parts of modified straw, 6-8 parts of fly ash, 7-9 parts of calcined gypsum powder, 10-14 parts of ore filler, 8-12 parts of silica sol, 6-8 parts of thermal insulation additive, 7-9 parts of polyvinyl alcohol, 4-6 parts of acrylic emulsion, 3-5 parts of modified nano additive, 5-7 parts of a gel material, 0.3-0.5 part of cellulose ether and 7-9 parts of fire-proof and flame-retardant additive. The thermal insulation board disclosed by the invention adopts a large amount of wastes, saves the resources, protects the environment, is high in material compressive strength, superior in weather resistance and excellent in humidity resistance, low in heat conductivity coefficient and good in thermal insulation effect, and also has a certain sound insulation effect at the same time; and furthermore, the preparation method disclosed by the invention has the advantages that the material cost is lower, the raw materials areeasy to obtain, the process is concise, the practical value is higher, and the application prospects are good.