To meet the demand for high-performance shotcrete in underground engineering, the effects of single and combined incorporation of nano-silica (NS) and nano-alumina (NA) on its workability, mechanical properties, and microstructure were investigated. Different mix proportions with varying dosages were designed, and slump as well as compressive strength at different curing ages (3, 7, and 28 days) were tested. Digital image correlation (DIC) technology, stress-strain curves, failure patterns, and scanning electron microscopy (SEM) were employed for analysis. The results indicate that single incorporation of 3% NS or 3% NA enhances strength, with 28-day compressive strength increasing by 15.9% and 11.1% respectively compared to the control group, though slump decreases. The combined incorporation system (total NS and NA dosage of 3%) demonstrates superior strengthening effects, with the optimal synergistic ratio of NS to NA at 2:1, achieving a 35.1% increase in 28-day compressive strength. DIC analysis indicates that the combined addition results in a more uniform distribution of cracks during specimen failure, a reduction in the width of primary cracks, a gentler descending segment in the stress-strain curve, and improved ductility. Microstructural analysis further confirms that NS and NA generate gel through pozzolanic reactions, exert micro-aggregate filling effects, and optimize the interfacial transition zone, leading to a denser microstructure. This study verifies that combined incorporation of NS and NA enhances the overall performance of shotcrete, providing an experimental basis for its engineering applications.