The invention provides a fly-ash fiber heat-insulation acoustic board and a preparation method thereof. Raw materials and weight percentages are as follows: 80.0-94.8 wt% of a fly-ash fiber, 3.1-10.0 wt% of an adhesive and 2.1-10.0 wt% of an additive. The fly-ash fiber heat-insulation acoustic board employs the fly-ash fiber as a matrix, wherein the raw material of the fly-ash fiber is fly ashes of industrial solid waste of power plants. The obtained product has volume density of 350-450 kg/m<3>, noise reduction coefficient of 0.45-0.65 and thermal resistance of 0.40-0.60 (m<2>.K)/W. The combustion performance of the fly-ash fiber heat-insulation acoustic board reaches to the requirements of A-grade non-combustible standard. The fly-ash fiber heat-insulation acoustic board has no materials poisonous and harmful to human and environment, such as formaldehyde, benzenes and the like, and can be widely applied in furred ceilings of indoor top surfaces and decoration and heat-insulation of walls for restaurants, hotels, commercial buildings, dwelling houses, office buildings, auditoriums, markets, movie theaters, subways, stations, factories, hospitals, airports, tunnels, etc.