With the diversified development of architectural space, transitional space is adopted more frequently in architectural design, and this space has resulted in an inevitable energy consumption. Until now, however, the definition of building transitional space has not been quite clearly given, and there is also a lack of relevant design standards and guidance. To further research transitional spaces for a better understanding of their energy-saving potential, this study has systematically reviewed existing studies exploring the thermal comfort requirements in building transitional spaces, including their definition, characteristics and functions, as well as the occupant's thermal comfort requirements. It found that the evaluation method of fully interior space is not suitable for building transition space, and people in such spaces are more adaptable and have a wider tolerance range than in fully indoor spaces. Furthermore, this study reviews the energysaving design strategy from the perspective of the thermal comfort of transitional space, focusing mainly on the reasonable use of the passive design strategy of large spaces, space's physical properties, the short-term thermal history. This study defines building transitional space more precisely; it serves as a reference for architects to improve the design of building transitional space and for researchers to improve the research on energy consumption in building transitional space and adjacent buildings.