Delayed ettringite formation (DEF) is considered a form of sulfate erosion within the cementitious material and is influenced by the high-temperature environment. The practical engineering will inevitably serve in the high-temperature geothermal environment. In this paper, the effects of temperature and admixtures on the strength, early shrinkage, pore structure and later volume evolution of concrete are studied, and the effective measures to restrain the DEF are discussed. The results show that the fly ash (F) and metakaolin (M) can mitigate the risk of volume expansion cracking caused by DEF after 210 d. When the concrete with 30% fly ash (F30), the expansion stress is reduced by 49%, and the expansion stress of F25M5 and F20M10 concrete with compound fly ash and metakaolin is reduced by 65% and 54%, respectively. No matter of pure cement group, cement + gypsum group or high-resistance sulfate cement + gypsum group, the change of expansion rate after 210 d was consistent with PC > > F30 ≈ F20M10 > F25M5. Taking into account the economic cost and reduction of delayed ettringite expansion effect, it is more economical and efficient to use the composite of Portland cement, fly ash and metakaolin than high sulfate resistance cement.