Abstract: The sclerotium of ettringite material is easily effloresced and lower its strength if it is exposed to the air. Its formation and weathering process are studied with methods such as accelerate chemical reaction, X-diffraction, SEM, TG and DT and also its physical chemistry characteristics are expounded. The reason of weathering is that carbon dioxide intrude into ettringite and decompose its structure, and thus loss its strength. This provide the basis for industrialized production and application of ettringite material.