为了更好地了解全球气候变化背景下，高海拔地区季节变化对生态和环境的响应机制，研究西藏季节早晚和长短等级划分指标变得尤为重要。根据1981—2023年西藏地区38个气象站点气温日资料，选择四季划分气温阈值6 ℃、17 ℃、17 ℃、6 ℃，探讨气候季节早晚和长短等级划分指标及其演变规律。结果表明：（1） 38站春、夏、秋、冬四季开始日期平均出现在4月21日、6月17日、7月17日、10月17日，时间长度平均为56 d、29 d、92 d、188 d。（2） 当年气候季节起止时间、时间长度整体上呈现“冬季标准差最小、夏季标准差最大”的特征。（3） 气候季节起止时间、时间长度早晚等级呈现“正常等级天数>略偏早晚、偏早晚等级天数>显著早晚、异常早晚等级天数”的特点，A指标更符合早晚和长短等级划分指标的阈值。（4） 西藏地区春夏季的开始日期有提前的趋势，秋冬季则有推迟的趋势。（5） 春季开始日期、冬季结束日期、夏季时间长度以正常等级为主，夏秋冬季开始日期、春秋季结束日期以早等级为主，春秋季时间长度以短等级为主，冬季时间长度以长等级为主，夏季结束日期以晚等级为主。研究结果可为气候资源管理、生态环境保护、人类生产生活等提供参考。

To better understand the response mechanisms of seasonal changes in high-altitude areas to ecological and environmental factors amid global climate change, it is crucial to study the indicators of seasonal early or late and length grade duration classification in Xizang. In this study, we analyzed daily temperature data from 38 meteorological stations in Xizang (1981-2023) using temperature thresholds of 6 ℃, 17 ℃, 17 ℃ and 6 ℃ for four seasons, to explore the classification indices and evolution laws of seasonal early or late and length grade. The results revealed the following: (1) The average start dates for spring, summer, autumn, and winter at the 38 stations were April 21, June 17, July 17, and October 17, with average lengths of 56 d, 29 d, 92 d, and 188 d, respectively. (2) The start and end times, as well as the lengths of the climatic seasons, exhibit characteristics of minimum standard deviation in winter and maximum standard deviation in summer. (3) The start dates, end dates, and length of the climatic seasons, as well as the start and end times and length of the four seasons, showed the following patterns: Normal>slightly early (late) and early (late)>significantly early (late) and abnormally early (late). A indicator is more in line with the threshold of the classification indicators of early or late and length grade. (4) In Xizang, the onset of spring and summer trends was earlier, while autumn and winter had late trends. (5) The start date of spring, the end date of winter, and the length of summer across the 38 stations were primarily classified as normal, whereas the start dates of summer, autumn, and winter, along with the end dates of spring and autumn, were mainly categorized as early. Conversely, the lengths of spring and autumn were mainly classified as short, while winter was predominantly classified as long, and the end date of summer was primarily considered late. These findings provide valuable insights into climate resource management, ecological protection, and the overall impact on human production and life.