Abstract: The mixing of micro-nano bubble water with shotcrete can improve the internal pore structure of shotcrete and enhance its mechanical properties. In this study, the nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) were utilized to study the influence of micro–nano bubble water gas type (air and CO₂) and shearing time on the porosity, pore size, average tortuosity, fractal dimension of pore structure, and microstructure of shotcrete. The test results show that the micro–nano bubble water can reduce the internal porosity of shotcrete, and the porosity of the micro-nano bubble water group with CO₂ gas is lower than that of the micro-nano bubble water group with air. The porosity of the sample is positively correlated with the shear time of the bubble water. the micro–nano bubble water can increase the proportion of gel pores in the specimens, and enhance the average tortuosity and fractal dimension of the pore structure. This indicates that the micro-nano bubble water can enhance the connectivity of the internal pore channels and the complexity of the pore structure of the sample. In addition, the shotcrete mixed with micro-nano bubble water has small pores, uniform pore distribution and denser internal structure.