Abstract: Four-point bending, uniaxial compressive and tensile tests were employed to explore the effects of the change of ambient temperatures (−30℃、0℃、30℃、60℃、90℃) on the mechanical properties of the ultra-high performance concrete (UHPC). The propagation of cracks during bending process was monitored by a digital image correlation (DIC) technology, and SEM and mercury intrusion porosimetry (MIP) were conducted to analyze the microstructure. The results show that the bending, compressive and tensile strengths of UHPC are within the range of 13.4-16.3 MPa, 121.5-133 MPa and 6.6-7.0 MPa, respectively, after subjected to different ambient change of temperatures. The tensile strain keeps almost consistent around 0.2%. Compared with standard temperature (30℃), the low temperature has little impact on the mechanical properties of UHPC, while the properties decrease with the temperature increasing, nevertheless, still at a higher level. The flexural strength and uniaxial strength present approximately linear relationship with proportionality coefficient of 2.3 at different temperatures. The matrix of UHPC at 30℃ is relatively denser, and thus possesses optimal mechanical properties.