In the context of global climate change and rapid urbanization, the urban heat island effect has been aggravated in many cities around the world. Green space can effectively improve the urban thermal environment. As land resources in the city are scarce, optimizing the layout of green space and making the limited green space offer a greater cooling effect has the important theoretic significance and practical worth. How to set the green patch size is one of the first considerations for optimizing the green space pattern. In this paper, we summarized exiting research about influences of green patch area on its cooling effect from the patch and landscape scale, respectively. At the patch scale, the cooling effect of green space nonlinearly enhanced with increasing patch area. Specifically, as the green patch size increased, the temperature decreased firstly and then leveled off. The optimal patch size, which had the strongest cooling effect per unit area green space, may exist. At the landscape scale, effects of the spatial layout of the size of green patch on the urban thermal environment varied considerably across studies. In addition, this paper pointed out some problems and shortcomings of existing relevant studies:1) Most of the studies focused on the statistical relationships between green patch area and temperature, while studies about the specific influence processes and mechanisms under those relationships were scare; 2) Most of the studies focused on the land surface temperature, but other thermal environmental indicators that directly related to human thermal comfort and health risk were ignored; 3) Small green patches, the main component of urban green space, were not included in most current studies. We further highlighted a few research directions or questions that should be paid attention in the future:1) Analyzing the internal mechanism of effects of green patch area on urban thermal environment from the perspective of cooling processes (shade and transpiration); 2) Exploring how the cooling efficiency (cooling effect per unit area green space) change with the patch area, and detecting the optimal patch size; 3) Investigating influences of urban structure (building) around the green space on the relationship between green patch size and its cooling effect. To explore and/or answer these research questions can effectively further reveal specific effects of green patch size on the urban thermal environment, and thus provide important scientific bases for planning the spatial layout of urban green space, enhancing the cooling efficiency of green patches, and improving the thermal comfort of cities.