This paper introduces the research results of the thermal stability and the delayed formation of ettringite in China and abroad. Aiming at the debate of the ettringite delayed formation condition of the massive shrinkage compensating concrete in the engineering field, the decomposition and delayed formation of ettringite were studied in simulated environments in massive concrete and other controlled curing environment. As UEA is the most applied expansive agent in domestic, the massive shrinkage compensating concrete mixed with UEA is selected as the research object. The test results show that, AFM appears in the research specimens when the inner temperature reach 80°C and the ettringite can reform under the condition of rich water supply after the concrete cooling to an ambient temperature. By comparing the test results of different curing environment, some points for attention during the construction of the UEA massive shrinkage compensating concrete are proposed.