Brackish water sprinkling can improve agricultural water use efficiency and alleviate water scarcity, but its impact on the rhizosphere fungal community structure of summer maize remains unclear. This study used high-throughput sequencing (fungal 18S rRNA gene) to explore the effect of mixed brackish-fresh water sprinkling with different mineralization degrees, focusing on the characteristics of topsoil fungal communities and their association with environmental factors. The results showed that 2 g L-1 brackish water significantly reduced the number of unique fungal species and richness in topsoil, altering the soil environment and community composition. It is involved in nitrogen transformation by regulating bacterial communities, and when combined with electrical conductivity (EC) and pH, these factors synergistically shape fungal community structure through the 'salt-nitrogen-pH' interaction pathway. Precipitation is a key factor affecting soil microorganisms; increased rainfall could raise microbial community abundance-based coverage estimator (ACE) richness by 1.9-4.6 times, yet it may also cause a decline in community diversity. The study confirms that brackish water with suitable mineralization can screen salt-tolerant fungi and alter community structure while maintaining diversity, providing a basis for water resource utilization and soil microecological regulation in arid and semiarid regions.