With the acceleration of urbanization, cities are facing an increasing number of environmental challenges, particularly the urban heat island effect, which causes elevated temperatures in densely built areas. Vertical greening, which involves the integration of plant-covered structures into urban landscapes, has been proposed as a potential solution to mitigate this issue. This paper analyzes the literature from the Web of Science database using CiteSpace bibliometric methods, and reviews the mechanisms through which vertical greening affects the outdoor thermal environment. The study focuses on the characterization factors of the outdoor thermal environment and the influencing factors of vertical greening. It summarizes various impacts of vertical greening on the thermal environment based on current research both domestically and internationally, and discusses the future prospects for sustainable built environments.