The invention discloses a fireproof sound-insulation building thermal-insulation composite board and a preparation method thereof. The fireproof sound-insulation building thermal-insulation composite board comprises the following raw materials in parts by weight: 19-25 parts of Portland cement, 15-25 parts of glass fiber, 16-20 parts of phenolic foam particle, 22-33 parts of polystyrene, 10-15 parts of coated vitrified microsphere, 11-23 parts of polyether glycol, 5-15 parts of bentonite, 9-18 parts of fly ash, 15-25 parts of sodium methane-silicate, 15-20 parts of magnesium chloride, 8-15 parts of redispersible latex powder, 3-8 parts of inorganic reinforcing fiber, 2-11 parts of butyl propionate and 5-14 parts of EPS (expandable polystyrene) particle. The glass fibers have very high toughness, so that the properties of the board are greatly enhanced in the use process, and the board has higher stability. Under the interactions of the Portland cement, glass fibers, phenolic foam particles, polystyrene, polyether glycol, fly ash, EPS particles and the like, the board has the properties of thermal insulation, water resistance and decoration. The composite thermal-insulation board has high heat stability, and is a composite thermal-insulation board with excellent properties.