To obtain a cement paste with high alternate ultra-high temperature (AUHT) resistance, this paper investigated the effects of metakaolin and graphite on the properties of cement paste. The results demonstrate that in the AUHT curing process, the ultra-high temperature changed the tetrahedral silicate structure in C-S-H from chains (Q(2)) to isolated silicate (Q(0)) or a dimer group (Q(1)), damaging the microstructure of C-S-H. Meanwhile, the substantial temperature difference caused the volume of each hydration product in the cement paste to vary unevenly, giving rise to high internal stress in the cement paste and thereby reducing its mechanical properties. However, metakaolin improved the mechanical properties of the cement paste by the filling effect and pozzolanic reaction. In addition, the layered structure of graphite accommodated the uneven variation of each hydration product in the cement paste at AUHT, reducing the internal stress and improving the mechanical properties of the cement paste. (C) 2020 Elsevier B.V. All rights reserved.