Abstract: Addressing the intensifying Urban Heat Island (UHI) effect in subtropical high-density cities, it is of great significance to investigate the synergistic cooling mechanisms between urban morphology and green infrastructure. Focusing on typical urban morphologies within the subtropical hot-humid climate region, this study utilizes the Local Climate Zone (LCZ) framework to construct six representative urban block models (LCZ1-LCZ6) covering varying densities and building heights. By coupling Grasshopper parametric modeling with ENVI-met microclimate simulations, the thermal regulation benefits of Extensive (EGR) and Intensive (IGR) Green Roof systems were systematically quantified across different urban morphologies. The model's reliability was validated through field measurements. The findings indicate: (1) The cooling efficiency of green roofs is strongly correlated with urban morphology, with IGR generally outperforming EGR; (2) Building height and density significantly impact cooling potential; the most significant cooling effect was observed in the low-rise high-density zone (LCZ3), where IGR achieved a maximum temperature reduction of △Ta: 1.04℃ at the roof level; (3) Lower building heights facilitate the settlement of cool air from roofs to the pedestrian level, thereby enhancing microclimate improvement below the canopy. This research reveals the non-linear thermal regulation laws governed by "building height-density-greening type," confirming that low-rise high-density morphologies combined with intensive green roofs offer the best adaptability. These findings provide a quantitative basis for green renewal and climate-adaptive planning in subtropical high-density cities.