The invention discloses a preparation method of an autoclaved aerated concrete block. The preparation method comprises the following steps: S1, preparing an additive A from aluminum powder paste, sodium sulfate and sodium abietate; and preparing fly ash, bagasse, juncus roemerianus powder, lime powder, gypsum powder and the additive A into ball billets, and curing to obtain lightweight aggregate; s2,preparing fly ash, ceramic tile waste, glass waste, quicklime and gypsum powder into a mixture; s3, preparing sodium hydroxide, rosin powder, triethanolamine and sodium silicate into an additive B; and S4, preparing a brick blank from the lightweight aggregate, the mixture, cement and the additive B, and maintaining the brick blank to obtain the autoclaved aerated concrete block. The invention further discloses the autoclaved aerated concrete block which is prepared by the preparation method of the autoclaved aerated concrete block. According to the autoclaved aerated concrete block, the construction waste, the household waste and the industrial waste are reasonably utilized, waste is turned into wealth, resource waste and environmental pollution are reduced, and the autoclaved aerated concrete block which is high in compressive strength and breaking strength and light in weight is prepared.