With the emphasis on building energy conservation in China, people's demands for quality of life and the comfort of building thermal environment have become the focus of attention. As a transitional space, the veranda has an important impact on the indoor thermal environment and building energy consumption. The main purpose of this study is to explore the thermal environment characteristics of the veranda space and its impact on the indoor thermal environment. Taking a building veranda in the hot summer and cold winter area as the research object, the measured data of indoor and outdoor thermal environment (temperature, humidity, wind speed, etc.) under different working conditions were collected. Through the data sorting and analysis, the thermal environment characteristics of the veranda space, the orientation of the veranda, the enclosure structure, the opening method of the doors and windows, the vegetation shading and other factors affect the indoor thermal environment. The measured results show that the transition space of the veranda has good thermal insulation effect in summer and can play an important role in reducing building energy consumption.