Abstract: Based on the daily minimum temperature data of 38 meteorological stations in Tibet from 1981 to 2020, the daily minimum temperature ≤0 ℃ was defined as the frost index, the spatial and temporal variation characteristics of the first frost date (FFD), the last frost date (LFD) and the frost-free period(FFP) in the Tibetan Plateau in the past 40 years were analyzed by using linear tendency estimation, Pearson coefficient, Mann-Kendall and dominance analysis. The results showed that: (1) In general, Tibet showed the distribution characteristics of early FFD, delayed LFD and reduced FFP from southeast to northwest, with significant vertical zonal characteristics of altitude. Compared with the average value from 1981 to 2010, at most stations, the FFD was postponed, the LFD was earlier, and the FFP increased. (2) Among the 38 stations in Tibet, there were 36 stations where the FFD was delayed and the LFD became earlier, and there were 35 stations where the FFP prolonged from 1981 to 2020. The FFD significantly delayed at the rate of 5.1 d·10 a⁻¹, the LFD significantly advanced by the rate of 3.4 d·10 a⁻¹, and the FFP significantly prolonged with a rate of 8.4 d·10 a⁻¹ during the past 40 years. (3) The FFD advanced in the altitude of 3000~3500 m, and the delay rate of the FFD increased with the increase of altitude in the area above 3500 m. The early characteristics of the LFD were similar in different altitude areas, especially in low altitude areas (2000~3000 m). The FFP increased at all altitudes, with the largest increase in areas above 4500 m. (4) In the 1980s, the FFD was earlier, the LFD was later, and the FFP was shorter. In the early 1990s, the FFD and LFD were slightly earlier, and the FFP did not change much. After entering the 21st century, the FFD was late, the LFD was early, and the FFP increased, especially in the 2010s. (5) The average of FFD, the LFD and FFP in Tibet had abrupt change in 2005, 1994 and 2003, respectively.