The Tibet Plateau is the "driver" and "amplifier" reflecting the climate change and also known as the " The world's third pole ". As an important part of the Tibet Plateau, the Three-river Source Region plays an important role in water conservation, climate regulation and ecological security. It is found that the high temperature phenomenon in Qinghai will become more frequent in the 21st century, and the warming rate will be greater than 0.30℃/10a. The increase of temperature will not only directly affect the change of extreme temperature, but also cause extreme climatic events such as high temperature, drought, rainstorm and flood, thus affecting the natural ecological environment and social economic activities. At present, studies on climate change in the Three-river Source Region mainly focus on the days of extreme climate events and the analysis of climate abrupt change, but there are few studies about the changes in frequency and intensity of extreme temperature events of different baseline climate states. Using the daily maximum and minimum temperature data of 23 national meteorological stations in the Three-river Source Region from 1961 to 2020, four climatic states were divided, including I (1961-1990), II (1971-2000), III (1981-2010) and IV (1991-2020). We analyzed the spatial and temporal distribution characteristics of threshold, frequency and intensity of extreme high temperature and extreme low temperature events in different climate states and explored the reasons for their changes. In terms of spatial distribution, the extreme temperature threshold basically shows that the higher the altitude, the lower the threshold, and gradually decreases from east to west. There are certain asymmetric warming characteristics in different climate states. The spatial distribution of the frequency and intensity of extreme high temperature is better than that of extreme low temperature, which shows the radially spatial distribution characteristics of the first and second climate states decreasing from west to east and the third and fourth climate states increasing from west to east; In terms of time variation, the frequency and intensity of extreme high temperature show an overall increasing trend of weak increase-rapid increase-slowdown of growth. However, the characteristics of time variation trend of frequency and intensity of extreme low temperature in different climatic states are not all consistent, which is manifested in significant increase in frequency, decrease in extreme-increase in frequency, increase in extreme-significant decrease in frequency and decrease in extreme. The decline of extremes is consistent with the implementation of ecological protection policies in the Three-river Source Region. After further analysis, it is found that the extreme temperature is teleconnected with multiple circulation systems, and there is a good causal relationship. The carbon emission of country also has a good lag response to the time series change of extreme temperature.