Abstract: Snow cover is one of the most active natural components in climatic system, and its variability has a major impact on global and regional climate change. Based on the daily data of snow cover, temperature, precipitation and wind speed at five meteorological stations in Chang Tang Nature Reserve of Tibet (CTNRT) from 1971 to 2017, the spatial-temporal evolution characteristics of snow cover days and snow depth were analyzed by using the methods of trend analysis and Mann-Kendall test analysis. Also, the correlation between the change of snow cover and climatic factors was discussed. The results showed that: the annual snow cover days of each station were 18.4- 67.0 in CTNRT, and the distribution increased from the west to the east. Meanwhile, with the increase of altitude, the snow cover days increased, the beginning day of snow cover was earlier, the terminal day of snow cover was delayed, and the duration of snow cover was prolonged. During 1971 to 2017, the annual snow cover days exhibited a significantly decreasing trend with a rate of 3.8 d/10 a, especially in autumn and spring. The annual maximum snow depth showed a decreasing trend with a rate of 0.53 cm/10 a. Additionally, the beginning day of snow cover was postponed with a rate of 11.3 d/10 a, the terminal day of snow cover was earlier with a rate of 11.0 d/10 a, the duration of snow cover was decreased with a rate of 23.3 d/10 a, in recent 27 years (1991-2017), this trend of change was even more obvious. According to the Mann-Kendall test, except in winter, the abrupt change of the seasonal snow cover days occurred in the first decade of the 21st century, the climate mutation point of the beginning day, terminal day and duration of snow cover all occurred in 2001. In conclusion, the decrease of snow cover days is mainly caused by the significant increase of mean temperature and the decrease of relative humidity, and the postponed beginning day and the earlier terminal day are not only related to the significant increase of temperature, but also closely related to the decrease of wind speed.