Abstract: Based on the daily average temperature data of four meteorological stations in southeastern Tibet from 1981 to 2022, the spatiotemporal variation characteristics of the four critical temperatures(≥0℃, 5℃, 10℃ and 15℃) were analyzed with the methods of linear trend estimation, Person coefficient, Mann-Kendall test and dominance analysis. The results showed that: (1)Affected by altitude, the four active accumulated temperatures(AAT) generally decreased in southeastern Tibet from southeast to northwest. The AAT(≥0℃, 5℃, 10℃and 15℃) ranged of 3161.4~4429.9℃·d, 2869.2~4018.0℃·d, 2273.3~3258.0℃·d and 608.8~2133.2℃·d, respectively. (2) In recent 42 years, the four critical temperatures in southeastern Tibet showed the trend of advancing the initial dates, delaying the final dates and prolongging the number of duration days. The smallest change range was observed with ≥10℃ critical temperatures, except for the initial date, the change range of ≥15℃ critical temperature was the largest. The lengthened duration days with ≥0℃ and ≥5℃ were mainly caused by the advanced initial date, while the increased duration days with ≥10℃ and ≥15℃ were mainly caused by the delayed final dates. As well as, the four AAT showed an extremely significant increase trend, with an increase rate of 123.81℃·d/10a, 136.71℃·d/10a, 76.22℃·d/10a, and 166.43℃·d/10a, respectively. (3) In terms of inter-decadal changes, the four AAT had obvious increasing of inter-decadal changes. The 2010s was the warmest decade in the study period, that of the four AAT increased by 174.9~437.2℃·d compared with the 1980s, with the largest increase in ≥15℃ AAT. Except for ≥10℃, the initial dates postponed, final dates advanced, and the duration days shortened during the period from 1980s to 1990s, while the first 20 years of the 21^st century were the opposite. (4) The M-K test showed that there was no climate mutation on the initial date and final date of ≥10℃, and the mutation time of other critical temperature indicators was mostly around 2004.