Spring maize is a major crop in semi-arid rainfed regions, where production is frequently constrained by seasonal drought and low early-spring temperatures. Although plastic mulching is widely used to improve the soil microenvironment, systematic evidence remains scarce regarding whether mulching timing can balance yield gains and greenhouse gas (GHG) emission mitigation. Using data from an 11-year field experiment, this study comprehensively evaluated the effects of different mulching timings on soil hydrothermal conditions, aggregate stability, microbial activity, GHG emissions, and maize yield. Results showed that early mulching, particularly spring frozen soil mulch (SFM), significantly improved soil hydrothermal conditions, increasing soil water storage by 46% and soil temperature by 13.2% during the sowing period compared with no mulch. SFM also increased the proportion of large aggregates by 28-36% and enhanced aggregate stability by 26-54%, while stimulating enzyme activity and root growth in the upper and middle soil layers, leading to a 65% increase in root length density. Consequently, grain yield and water use efficiency increased by 64.9% and 79.6%, respectively, relative to the no mulch. Despite elevated COQ and NQO emissions under mulching, the carbon footprint per unit yield under SFM decreased to 2.30 kg COQ-eq & sdot;kg-1 , which was significantly lower than that of conventional pre-sowing mulching. Structural equation modeling (SEM) further revealed that mulching timing co-regulated yield formation and environmental effects through the pathway "soil structure-enzyme activity-root development." In conclusion, SFM achieves the synergistic goals of high yield, high resource use efficiency, and low carbon emissions in semi-arid regions. These findings highlight the potential of optimizing mulching timing as an effective strategy for sustainable rainfed agriculture.