The invention relates to a high-volume paper mill sludge aerated concrete block and a preparation method thereof. The aerated concrete block is prepared from the following raw materials: paper mill sludge, quicklime, PO42.5 cement, aluminite powder, silica fume, gypsum, sodium chloride, sodium nitrite, sodium sulfate, calcium chloride, urea, methacrylic acid, a silane coupling agent, calcium gluconate, triisopropanolamine, fatty glyceride, hydroxypropyl methyl cellulose, calcium stearate, a Z5 concrete hardener, polycarboxylic acid and potassium permanganate. According to the preparation method of the high-volume paper mill sludge aerated concrete block, by using the paper mill sludge as a main raw material, the prepared aerated concrete block has the advantages of high strength, good toughness, light texture, good insulation effect, low water absorption rate, good corrosion resistance, good water resistance, high surface hardness, good freeze-thaw resisting effect, low production cost, capability of carrying out harmless treatment on the paper mill sludge and the like.