The outdoor thermal environment (OTE) is closely related to sustainable urban development and human living, and related research has attracted widespread attention. The research hotspots and research frontiers were obtained using CiteSpace to analyze 4473 relevant studies published in English from the Web of Science (WOS) core database from 1998 to 2023. The results show that (1) Hong Kong Polytechnic University, National University of Singapore, Chinese Academy of Sciences, Tsinghua University, and Harbin Institute of Technology are important in OTE research. China has the largest number of publications in the field of OTE, but the United States has the greatest centrality and significant influence. (2) The focus of OTE keyword clustering research is divided into four main categories: thermal environment perception, the thermal environment index, thermal environment quality, and thermal environment optimization. (3) The frontiers of OTE research have changed from focusing on environmental quality, thermal perception, numerical simulation, urban space, and thermal adaptation to thermal mitigation, energy conservation, energy consumption, and optimization strategies. Visualization research in the field of OTE helps to provide references for the direction of future research on improving climate change, human thermal comfort, urban planning, and pre-planning.