Urban green infrastructure (UGI), a multiscale, multi-type, and multi-function network composed of green elements, plays a pivotal role in alleviating the increasing temperature in urban areas. Nevertheless, systematic discussions about the research methodology, mechanisms, and influencing factors of cooling effects of UGI are rare in the literature. Thus, this chapter reviewed the progress on the cooling effects of UGI in terms of research methods, physical mechanisms, and influencing factors. Moreover, this chapter also discussed the limitations, challenges, and future works about cooling effects of UGI, providing references for the researchers and practitioners concerning UGI and mitigation pathways of urban heat island.