Sulfoaluminate-type Expansive Agent may increase the risk of DEF (Delayed Ettringite Formation) due to high content of ettringite formed during hydration.The effect of fly ash and silica fume on DEF in mortar with Expansive Agent treated at different temperature (20, 70, 80 and 90℃) are discussed in this paper.The research is based on deformation test and SEI.Results shows that fly ash can reduce the deformation but need a high replacemen level and silica fume affects slightly, as they work in different mechanism.