Room air conditioner (RAC) is the important facilitly to improve the indoor thermal environment in the Yangtze River Basin in China. However, the current study couldn't get an in-depth stady of the set temperature behavior of the RAC due to the limitation of the data acquisition method. In order to get the set temperature behavior of the RAC in the Yangtze River Basin, the distribution of the set temperature, the adjustment behavior of the set temperature, the relationship between the set temperature and the time of a day and the relationship between the set temperature and outdoor air temperature were statistically analyzed based on the big monitoring data platform. After the data processing, tens of thousands of times of RAC running data in summer and in winter from a total of 575 room air conditioners in Chongqing, a total of 430 room air conditioners in Wuhan, a total of 540 room air conditioners in Shanghai was obtained, which was aimed at three typical cities in the Yangtze River Basin. The results show that there are some differences between the set temperature behavior and its adjustment behavior in three typical cities. Besides, the short time requirement of the lower set temperature (below 26℃) exists in once running period in summer and the set temperature is also related with the time of a day and the outdoor air temperature.