Abstract: In order to study the mechanical properties of ultra-high toughness cementitious composites (UHTCC) after temperatures of 200-−100℃, UHTCC with different fiber volume content was designed. The basic mechanical properties of UHTCC after medium-high temperatures and cryogenic temperatures were tested, and the mechanical properties of UHTCC after medium-high temperatures and cryogenic temperatures were evaluated by parameters such as strength and deformation of UHTCC. The results show that the incorporation of fibers can effectively improve the brittleness of the material and enhance the toughness of the material. The temperature effect makes the initial defects appear inside the material, which has a significant effect on the mechanical properties of UHTCC, and the effect of low temperature is significantly higher than that of high temperature. When the temperature is reduced to −100℃, the strength of UHTCC is reduced by about 71% at most, and the deformation is reduced by about 92% at most, but the temperature has no significant effect on the Poisson's ratio of UHTCC. On this basis, the regression model of axial compression and axial tensile stress-strain relationship of UHTCC after medium-high temperatures and cryogenic temperatures is proposed, which provides a reference for the performance design and engineering application of UHTCC materials at extreme temperatures.