Abstract: In order to further understand the climatic characteristics of hail in Chang Tang National Nature Reserve Region of Tibet (CTNNRR), put forward some disaster reduction countermeasures and reduce the hail disaster losses, the spatial and temporal evolution characteristics of hail days in CTNNRR from 1971 to 2017 was analyzed with trend analysis, Mann-Kendall test method and Morlet wavelets analysis method based on the hail data of the 5 meteorological stations in CTNNRR. The results shows that: On a multi-year average, the hail days ofSeachSstation were 1.6-28.1 days in CTNNRR, and the distribution was decreasing from western to eastern. Temporally, the hail occurred mainly from June to September, most frequent in August, and the hail occurred mostly during 12 to 18 o"clock with duration of 1 to 10 minutes. The hail days exhibited decreasing trend with a rate of 3.4 d/10a in CTNNRR during the recent 47 years, especially in Xainza with a decreasing rate of 7.0 d/10a. On the decadal scale, the hail days was more during 1970s to 1990s and less in the 2000s. According to the Mann-Kendall test, the abrupt change of the annual, summer and autumn hail days occurred in the middle and later periods of 2000s, indicating a change from the more period to the less one. There was obvious periods of 3 years for the hail days in spring and autumn, together with of 5 years and 8 years in spring. The decrease of hail days was related to the significant increase of mean temperature and the decrease of daily temperature range.