This paper focuses on the working and mechanical properties of UHPC under the conditions of different binder sand ratios. Mercury-in-pressure (MIP) was used to characterize the effect of different binder sand ratios on the pore structure evolution of UHPC hydrated slurry, and the types of hydration products and microstructure change rules in the slurry were analyzed with the help of thermal analysis (TG-DTG) and SEM. The results showed that the extensibility of UHPC decreased with the increase of the binder-sand ratio(0.9–1.2), and when the binder sand ratio was 1.1, the mix flowed relatively well and had the best mechanical properties at all ages. With the increase of the rubber-sand ratio, the flow index of the mix is getting larger and larger, and the hydrated slurry all shows the trend of slurry thickening. When the binder-sand ratio is 1.0 and 1.1, the hydration process of the slurry is faster, the generation of hydration products is high, there are more gelling pores and mesopores, relatively few macropores, and the slurry densification is higher, resulting in the best mechanical properties of the hardened slurry, especially when the binder-sand ratio is 1.1.