There is a certain necessary connection between urban thermal environment and urban factors. In order to study the connection, this paper analyzes the main urban factors impacting human comfort degree from the perspective of human comfort degree. We adopt the way of thermal climatic index to calculate the uncomfortable days with high temperatures in Hangzhou from 1980 to 2017, and sum the change trend. By means of gray relational analysis of entropy-based optimization, we determine the weights of different factors and analyze the connection between urban factors and uncomfortable days with high temperature. The results are as follows. First, over the past 38 years, the average uncomfortable days with high temperature in Hangzhou are 30.6 d, and the climate tendency rate is 6.87 d·(10 a)-1, showing a significant upward trend. The interdecadal variation changes dramatically. The uncomfortably days with high temperature mostly appear in July and August and notably the uncomfortable days with high temperature appear more frequently from 1992 to 1993. Second, according to the results of gray relational analysis of entropy-based optimization, among 12 index factors, the weight of the occupying areas of secondary industry is the biggest, with highway passenger volume standing the next. Population density accounts for the smallest proportion.Third, highway passenger volume and the weight of occupying areas of secondary areas strongly correlate with days with high temperature, while the other ten factors such as garden area, green coverage area of built-up area, and population density correlate with days with high temperature moderately. In conclusion, gray relational analysis has advantages in the prediction of multiple factor connection. It can effectively analyze the main urban factors impacting days with high temperatures and has some values in application.