Abstract: The mechanical properties of ultra-high-performance concrete (UHPC) after high temperature were studied by static and dynamic compression and splitting tests. Moreover, the microstructure of UHPC after different temperatures was observed by scanning electron microscope (SEM), which further revealed the reasons why the changes take place in mechanical properties of UHPC after different high temperatures. Five target temperatures were set, i.e., 25 ℃ (room temperature), 200 ℃, 400 ℃, 600 ℃, and 800 ℃, and a total of 120 specimens were tested. The results show that both the static and dynamic strength of UHPC increase first and then decrease with the temperature. At the same impact velocity, the compression and splitting impact toughness of UHPC also increases first and then decreases with the temperature. However, when the impact velocity is weak, the effect of temperature on the impact toughness is not significant. The formula for the variation range between strain rate and dynamic increase factor (DIF) was fitted in this study. The tensile dynamic increase factor (TDIF) of UHPC decreases first and then increases with the temperature (except 800 ℃). However, TDIF under different target temperatures (except 800 ℃) decreases with the increase of splitting strength, which shows that the strain rate enhancement effect of UHPC decreases with the splitting strength of UHPC.