Micro-nano bubble water (MNBW) has the characteristics of large specific surface area, good stability and high activity of water molecules. MNBW can be used to mix shotcrete to improve the physical and mechanical properties of shotcrete. MNBW was selected as the mixing water, and the effects of MNBW bubble gas type, MNBW shear time, MNBW content and alkali-free liquid accelerator content on the setting time of cement paste and the mechanical properties of cement mortar were studied. The digital image acquisition technology was used to explore the interface crack propagation law of cement mortar during uniaxial compression. The results show that MNBW (especially MNBW containing CO₂ bubbles) can significantly promote the hydration reaction of cement and shorten the setting time of cement paste. The compressive strength and flexural strength of cement mortar increase with the increase of MNBW content and curing age, and increase first and then decrease with the increase of MNBW shear time. In the process of uniaxial compression failure, the load value required for the initial crack initiation of different mixed water specimens from large to small is CO₂ bubble MNBW group, air bubble MNBW group, and tap water group.