The urban heat island(UHI) effect poses a significant threat to human health, and together with the continuously developing central urban environment towards high-density and high-intensity, brings new challenges and demands to the construction of green infrastructure and healthy development of cities. Green roofs, which do not take up additional construction land, have become one of the most important strategic measures to improve the urban thermal environment. In response to the low correlation between current roof greening cooling simulation and actual planning and construction processes, as well as the lack of in-depth analysis of cooling characteristics, based on three decisive influencing factors: construction scale, construction sequence, and construction type, a method transformation has been achieved from constructing ideal scenarios for roof greening cooling effects based on abstract experimental thinking to constructing actual scenarios based on planning and construction decision-making perspectives. The quantitative characteristics of the cooling effect of green roofs in high-density urban neighborhoods in different scenarios were examined from the whole to the local using ENVI-met. The results show that: (1) the cooling intensity of green roofs increases linearly with the increase of construction scale, and the cooling effect of green roofs in the same scale of podium construction is much higher than that of public and commercial buildings. (2) Green roofs built in more urgent area of thermal environment improving can be local cooling, but from the overall point did not get a higher cooling benefit; when the new roof greening location is similar, the growth of cooling effect can be slowed (3) At the same height, The cooling intensity of green roofs on localized plots shows an exponential decay as the distance from the green roof boundary increases; with the increase in the cooling intensity of the green roof with the distance from the green roof boundary. The decay rate of cooling intensity parallel to the wind direction is significantly slower than that perpendicular to the wind direction; (4) The average cooling intensity of intensive green roofs in the study area grid is 4.69 times higher than that of rough green roofs, which is more cost-effective in terms of cooling compared to its price. Based on the simulation results above, targeted planning strategies are proposed,providing a scientific basis for the construction practice of green roofs in high-density neighborhoods, in order to improve the thermal environment of high-density neighborhoods, promote the health and well-being of urban residents and the healthy transformation of high-density cities.