Urbanization has transformed the spatial pattern of urban land use by reducing green spaces. An increase of air temperature directly affects forest vegetation, phenology, and biodiversity in urban areas. In this paper, we analyzed the characterization of changing patterns and Urban Heat Distribution (UHD) in Seoul, based on a spatio-temporal assessment. It is necessary to understand green spaces changes, and this understanding is essential for monitoring and assessing green spaces functions. In addition we estimated the effect of green space on urban temperature using Landsat 7 ETM+ imagery and climatic data. Results of the assessment showed that UHD creates differences in the spatial and temporal extent of temperature reducing effects due to differences in urban green space. The ratio of urban heat area decreases rapidly from green space boundary. And it shows that the urban green space plays an important role for mitigating urban heating in central areas. This study demonstrated the importance of green spaces by characterizing the spatio-temporal variations of urban green spaces in cities.