The retention and release behavior of NH4HSO4 in cement fly ash paste and the effect of retention and release on cement fly ash system were studied by the simulation method of adding NH4HSO4. The results show that the decomposition of NH4HSO4 in denitration fly ash results in the release of ammonia and the retention of NH4+ and NH3.H2O . When 30% denitration fly ash is added into cement, the remaining NH4HSO4 will reduce the pH of cement fly ash system to a small extent and concentrate in the first 1h, and the influence on cement hydration will also concentrate in the early stage, which is manifested as reducing hydration exothermic peak and delaying the emergence of exothermic peak. In the later stage, with the continuous hydration, there is no influence on cement hydration heat and hydration products. With the increase of NH4HSO4 content, the release rate of ammonia gas in cement fly ash system increases, but the retention ratio of ammonia is also larger. The release of ammonia will increase the porosity of cement fly ash system and the number of large pores.The increase of ammonia content,mixing and water cement ratio of denitration fly ash will accelerate the release rate of ammonia.