The invention discloses an aerated concrete block and a preparation method thereof, and relates to the technical field of building materials. The aerated concrete block is prepared from the following raw materials: modified pulverized fuel ash, slag Portland cement, kaolin, polypropylene fibers, baryta feldspar powder, aerated aluminum powder, heulandite powder, tetrachloroisophthalonitrile emulsion, benzoic acid, ethyl paraben, dimethyl sulfoxide, an early strength agent, a water reducing agent, a water addition agent, a foaming agent and a foam stabilizer. The preparation method comprises the steps of firstly, evenly stirring and mixing the raw materials to prepare slurry, then carrying out pouring, initial curing treatment, cutting and autoclaved curing on the slurry to obtain the aerated concrete block. The aerated concrete block is high in compression strength, good in heat resistance and sound insulation, small in drying shrinkage value, excellent in water resistance, simple to prepare, wide in raw material sources, and low in cost, thus being suitable for being popularized and used.