Trees have many functions for human lives, such as mitigating the heat release inside the city produced by human activities. This study aims to analyse the impact of trees cooling effect on the microclimate of green open spaces, especially in urban areas. Envi-met is an environment simulation software that was created as a temperature and humidity monitoring method to evaluate the impact of cooling on green open space. It proves that trees can lower the room temperature by 2 to 4 °C depending on the presence of sunlight compared to one planted only with shrubs. It can be concluded that not all green areas can reduce the surface temperature of the environment; it depends on the type of cover planted, the larger the tree canopy, the higher the effectiveness of temperature reduction. This issue can be used by the government as a guide in issuing further policies in every development, especially the number of trees that must be provided in a city to reduce the air temperature in both public and private spaces to mitigate environmental changes that occur, especially in urban areas.