Abstract: By analyzing average daily air temperature and relative humidity data from 1951 to 2009, the daily human comfortable degree of Nanjing in the past 60 years was determined calculated. Based on this calculation, the comfort grades were formulated. The results showed that Nanjing was getting more comfortable in general. The most comfortable months in Nanjing were May and October, the more uncomfortable month was January, and from late July to early August was the hottest uncomfortable period. The start and end time of the most comfortable day in spring was in advance. In the meantime, the start time of more thermal uncomfortable day in summer was in advance and the end time was postponing. The start time of the most comfortable day in autumn was postponing and the end time was in advance, the most comfortable days were reducing, in the mean time, the start time of the thermal comfortable day in autumn was in advance and the end time was postponing. The start time of the extremely cold uncomfortable day in winter was postponing and the end time was significantly advanced, the extremely cold uncomfortable days were reducing.