<p>The possibility of engineering structures bearing the external loads with high loading rates (such as impact, shock, and explosion) is increasing, resulting in higher strain rates (change rate of strain) for concrete materials. There is a lot of studies about the mechanical properties of ultra-high-performance concrete (UHPC) under impact loads. Among them, the dynamic increase factor (DIF, the ratio of dynamic property to quasi-static property) is one of the most important factors for evaluating the dynamic mechanical properties of concrete. This paper presents a systematic&#xa0;review of the mechanical properties of UHPC under compression at strain rates from 0.0003 to 300 s⁻¹. Besides, mechanical properties of UHPC under tension are also reviewed at strain rates from 0.00033 to 150 s⁻¹. Furthermore, the mechanisms of the strain-rate effects on UHPC are studied. The analysis results show that the strain-rate sensitive for strength of UHPC is lower than that of ordinary Portland cement concrete, resulting in the conventional DIF models of ordinary concrete are not suitable for UHPC. Therefore, the transition strain rates between high and low strain rates for compressive and tensile strength are determined separately. After that, two new DIF models of UHPC for compression and tension are established based on the existing studies with high precision, respectively. The difference of strain-rate between compression and tension is discussed. Besides, the strain rate effects of other properties under compression and tension including failure modes, strength, stress–strain curve, peak strain, and elastic modulus are discussed. This paper also proposes a research direction for future studies on UHPC under dynamic loads.</p>