The Three Rivers Source Region (TRSR) is an important water source and ecological reserve in China, and revealing the changes in the characteristics of its freeze-thaw index can provide a scientific basis for the assessment of the local permafrost environment as well as the response to climate change. In this study, the temporal and spatial characteristics of the Air Freezing and Thawing Indices (AFTI) in the TRSR for the period 1979-2022 were analyzed using the day-by-day air temperature data from a high-resolution near-surface meteorological forcing dataset for the Third Pole region (TPMFD) by means of air freezing and thawing index and other methods. The results show that the mean value of the freezing index in the TRSR over the past 44 years is 1 930.23 °C·d, exhibiting a spatial pattern of gradually decreasing from west to east. In contrast, the thawing index displays an opposite spatial pattern with an average value of 879.25 °C·d. Overall, the freezing index in the TRSR has shown a fluctuating decreasing trend at a rate of -10.01 °C·d/a for the last 44 years with an abrupt change in 2001, while the thawing index has shown a fluctuating increasing trend at a rate of 6.29 °C·d/a with no significant abrupt change. Altitude, as a key factor of freezing and thawing indices in the TRSR, showed a significant correlation, and for every 100 m increase in altitude, the thawing index in the TRSR decreased by about 87 °C·d, and the freezing index increased by about 107 °C·d.