青海三江源区是全球气候变化的敏感区和生态环境脆弱区，目前正面临着冻土退化的问题。本研究基于三江源区18个国家气象站1961—2021年气象观测资料，对气候变暖前后季节冻土冻融特征进行对比分析。结果表明：三江源区年平均气温为-0.34 ℃，呈东高西低分布，总体以0.38 ℃·（10a）^-1的速率上升，并在1997年发生突变，突变后气温显著升高。平均年最大季节冻结深度为142.5 cm，自西北向东南减小，总体以2.4 cm·（10a）^-1速率退化，与变暖前相比减少了11 cm。平均地表冻结初日为10月24日，以1.0 d·（10a）^-1速率推迟，平均地表冻结终日为5月18日，以3.3 d·（10a）^-1速率提前，与变暖前相比，地表冻结终日提前了12 d，地表冻结初日推迟了14 d。季节冻土平均冻结时间为133.9 d，呈西高东低分布，总体以1.9 d·（10a）^-1速率减少，与变暖前相比减少了8.8 d。年最大冻结深度及冻结时间分别在2004年和2002年发生突变，相比气温均有一定滞后。这说明，季节冻土在受气温变化影响同时，还受地形、人类活动等其他因素影响。该研究揭示了三江源区季节冻土冻结作用弱化的现象，研究成果可为应对气候变化、工程建设等提供参考。

The Three-River Source Region （TRSR） is a sensitive area of global climate change and a fragile ecological environment， and is currently facing the problems of permafrost degradation. This study analyzed the freezing and thawing characteristics of seasonally frozen ground in the TRSR before and after climate warming from 1961 to 2021 based on observations from the 18 national meteorological stations. The results show that： （1） The mean annual air temperature （MAAT） in the TRSR is -0.34 ℃ during 1961 to 2021， which is high in the east and low in the west， and an overall increase of 0.38℃·10a^-1 was observed， and the sudden change occurred in 1997， and the temperature rises significantly after the mutation； （2） The mean annual maximum seasonal freezing depth is 142.5 cm， which decreases from northwest to southeast， and degrades by 11 cm with an overall rate of 2.4 cm·10a^-1 in comparisons of that before 1997； （3） The first day of ground surface freezing is averaged on October 24， which is postponed at a rate of 1.0 d·10a^-1， and the ground surface freezing is averaged on May 18， which is advanced at a rate of 3.3 d·10a^-1 and 12 days earlier， and the first day of ground surface freezing is delayed by 14 d compared with before 1997； （4） The onset freezing of near-surface shallow soils （0~3.2 m） is 133.9 d， which exhibits a spatial tendency of west-high and east-low， and the overall decrease rate is 1.9 d·10a^-1， which has decreased by 8.8 d compared with before 1997； （5） The annual maximum freezing depth and the onset of freezing of near-surface shallow soils changed abruptly in 2004 and 2002， respectively， and the mutation time had a certain lag with the temperature. The study implicated that seasonally frozen ground is jointly affected by climate warming and anthropogenic activities. This study revealed the degradation of seasonally frozen ground in the TRSR， which may provide references for climate change and engineering construction.