With nonlinear similarity method, we divised the seasons for whole China on the basis of daily mean temperature, pressure, relative humidity and precipitation at 752 stations for the period 1961—2008, and analyze the seasonal division for eight regions of China and seasonal times. In addition, the relevant statistic data are established which contain the annual variation in frequency of extreme temperature in China. By combining these two research findings, their relationship over the past 48 years is found through correlation analysis and sensitivity test. The results show that: (1) in most areas of China, the spring and summer starting time move up, their durations are extended, autumn starting time changes a litter, and its duration is extended, while winter is pushed back the starting time, and its duration is shortened. (2) With the summer extending, the frequency of extreme high temperature is increased in most areas of China except East China, while the shortening of winter results in the frequency of extreme low temperature declining markedly. (3) The existence and the annual change of extreme high and low temperature are the reason why the lengths of summer and winter change, and they are also the main reason why the substantial fluctuations of the lengths of summer and winter take place.