Under the background of urban intensification, the moderating role of green space patterns on urban heat island (UHI) effects has become a significant topic in urban planning and ecological management. This study uses Nanjing as a case study. It analyzes data from the Urban Density Index (UDI), Land Surface Temperature (LST), Green Space Index (GSI), and Landscape Pattern Index for 2012, 2016, and 2020. We employ Moran’s I spatial autocorrelation analysis and a coupling coordination degree model to systematically explore the moderating mechanisms of green space patterns on the UHI effect and their temporal-spatial evolution. The findings demonstrate that urban intensification significantly exacerbates the UHI effect, with a positive correlation between UDI and LST. Meanwhile, GSI shows cooling potential through spatial optimization. Green spaces mitigate UHI effects mainly through evapotranspiration, shading, and continuous distribution, with areas like Zijin Mountain showing low LST and high GSI distributions, which validate their cooling effect. Landscape pattern analysis indicates that the negative correlation between the Largest Patch Index (LPI) and LST has strengthened, while fragmented green spaces limit cooling effects. The coupling coordination degree increased from 0.5 in 2012 to 0.6 in 2020, indicating a gradual improvement in the coordination between green spaces and the thermal environment. However, the coordination in the central urban area remains low. To optimize green space layout and enhance its cooling effectiveness, this study suggests improving green connectivity, expanding contiguous green areas, and promoting green roofs, providing a scientific basis for UHI mitigation in Nanjing and similar cities.