Thermal environment in urban public space is considered as an important factor affecting thermal comfort of human beings. In the whole year, thermal environment in public space of the city in hot-summer and cold-winter zone changes dramatically, which has an effect on human thermal comfort. In this study, three typical public spaces including street, park and square of Changsha were selected for a long-term experiment of thermal environment. Based on the analysis of four significant thermal environment parameters-air temperature, relative humidity, global temperature and wind speed, seasonal characteristics of thermal environment in urban public space were obtained. The results show that the characteristics of urban thermal environment are determined by natural climate, while the physical structure of a city has essential impact on the changes of local outdoor thermal environment. Affected by plants (trees) and water (Xiangjiang river) air temperature of the street along the street is much lower, relative humidity is higher and solar radiation is weaker in most of the year. Compared to the street along the river, air temperature of the square is higher and solar radiation is stronger.