Abstract: The changes in annual, winter, spring, summer and autumn air temperatures over China in the last 50 years are analyzed through statistical diagnosis and the focus of the study is put on the difference of change and warming process between 1990s and 1980s. The results show that the annual temperature anomaly has an increasing trend in the last 50 years, but the inter-decadal change in annual temperature is not remarkable before 1990. The mean temperature from 1991 to 2000 is much higher than those in the other decades. Their 10-year means are – 0.12oC from 1951 to 1960, – 0.10oC from 1961 to 1970, – 0.04oC from 1971 to 1980, 0.14oC from 1981 to 1990, 0.57oC from 1991 to 2000, respectively. The difference between the mean from 1991 to 2000 and the mean from 1981 to 1990 is of statistical significance with a confidence level of α=0.05. The linear trend coefficient of the mean temperature over China is only 0.008oC per year before 1990, but 0.02oC per year from 1991 to 2000. The beginning of warning was at the end of the 1980s and the warming speeded up in the 1990s in China, during which period a transition from clod to warm occurred in the south of the Changjiang River Valley. The change trend of temperature and the warming processes is the 1980s and 1990s were very different for four seasons. In winter, the beginning of warming was the earliest with the strongest argument and the longest duration. The main contribution to the steep warming during the 1990s comes from the long-lasting higher temperature in winter and the temperature rising in spring, summer, autumn, especially the ever-increasing warming argument and the ever-expanding warming areas in spring and summer. Only 59% and 31% of stations over China have an increasing trend in spring and summer before 1990, but 83% and 50% from 1991 to 2000.