Autoclaved Aerated Concrete, in short as AAC, is a new type of light weight, multi-cells construction material. The features include simple in processing, fast in construction, low density, heat insulation, processibility, earthquake resistance and sound resistance properties. AAC is made from silicon material (silica sand, or recycled fly ash and silica gangue) and calcium material (lime, Portland cement), mixing with a small quantity of foaming additive (aluminum powder). The main raw material is fly ash or silicon sand. Fly ash is main waste from electricity power station. Up till now, AAC is the best choice to replace clay brick. It will dig too much clay to produce clay brick to destroy the earth terribly.With abundant air cells and micro apertures inside the aerated brick, it has good performance of heat insulation and preservation. In addition, the most prominent advantage is its plasticity. Due to the lightness and the lower hardness, AAC units are available in numerous shapes and sizes according to the real construction usages and customer’s requirements. From the manufacturing processing and application with good insulation, AAC is a kind of green building material.