As a proven strategy for urban microclimate enhancement, green roofs demonstrate significant potential in mitigating unpredictable meteorological events and disaster resilience. While existing research predominantly focuses on green roofs’ energy-saving and local environmental benefits, their broader climate regulation mechanisms remain underexplored. This study uses the ENVI-met simulation platform to explore how green roofs regulate outdoor microclimates. The study establishes causal linkages between critical green roof parameters (LAI, substrate moisture gradients) and environmental drivers (meteorological forcing, building morphology). Comparative analysis reveals intensive systems exhibit greater efficacy in simultaneous heat mitigation, humidity buffering, and thermal comfort enhancement relative to semi-intensive/extensive systems. Increasing LAI enhances cooling and humidification, but the benefits level off after a certain point. Substrate moisture content has a significant impact during the day but less so at night. Moderate wind speeds (around 2 m/s) and clear weather conditions support green roof performance, especially during the day. The height of buildings also affects microclimate benefits, with lower buildings creating more favorable conditions. Meteorological factors have the most significant influence on green roof performance, followed by component parameters, while building height and layout have a smaller impact. Green roofs improve microclimatic conditions during the day, but their impact decreases at night, highlighting their importance for urban environmental enhancement. This study delivers the first systematic examination of green roofs’ transboundary microclimate regulation mechanisms—particularly through LAI, substrate moisture, wind-buildup interactions—filling a critical knowledge gap in urban climate science.