One of the key points for developing ultra-high performance concrete(UHPC) with good construction is to determine the suitable water-binder ratio. Based on the premise that the typical raw materials and mix ratio of 150MPa grade UHPC remained unchanged (except water consumption), the influence of water-to-binder ratio (0.15~0.2) on the construction and mechanical properties of UHPC were studied. Through relevant tests, the extension degree, compression resistance, bending strength, four-point bending stress-deflection curve, and equivalent tensile stress of UHPC under different wet mixing time (full wet mixing time, static stop for a period of time) were obtained. Subsequently, the variability of compressive strength and flexural strength results were analyzed; Using the stress-deflection curve, the index of bending toughness was obtained based on the standard method. At the same time, an improved method for calculating flexural toughness index of UHPC was proposed. The test results show that the full wet mixing time of UHPC is 6 min. The extensibility of UHPC increases linearly when the water-to-binder ratio increases from 0.16 to 0.19. And at this time,the average extensibility rate of UHPC increases to 109 mm with the water-to-binder ratio increases by 0.01. The extensibility loss of UHPC is 40mm, and the loss rate is only 5.9%, when the water-to-binder ratio and standing time are 0.19 and 4h. The compressive strength, flexural strength and flexural toughness index of UHPC all increase first and then decrease with increasing of water-to-binder ratio, and when the water-to-binder ratio is 0.18, 0.16 and 0.16 respectively, the three mechanical properties reach the best. The stress-deflection curve before the stress peak is an atypical full convex curve. The strength of visible first crack is about 0.85 times that of flexural strength. The flexural toughness of UHPC is good, so it is better to use visible first crack deflection as the initial deformation reference to calculate the flexural toughness index. In order to ensure the good construction and mechanical properties of UHPC, the wet mixing time and water-to-binder ratio should be 6min, 0.18 or 0.185 respectively.