The source region of the Yellow River is in the northeastern area of Tibetan Plateau (32°30'~36°12'N, 95°50'~103°30'E). This area is arid with a plateau-continental climate, which is in drought throughout the year. Its climate is affected by the plateau monsoon. This important region of the Tibetan Plateau has experienced changes in geographic environment and climatic conditions. These changes play a significant role in the Tibetan Plateau climate change, and will lead to problems in the social and economic development of Northwest and North China. It is important to develop new tree-ring chronologies in this region,in order to recognize climatic variation in the past. Tree-ring width chronology was created by Sabina przewalskii Kom. which collected in Xueshan Township of Maqen County of Qinghai Province (XS: 34°77.293'N, 99°67.817'E; 3780~3811m). In total, 51 cores/26 trees were collected. All samples were surfaced, cross-dated and measured according to standard dendrochronology techniques. Three types of tree-ring width index chronologies were created: Standard (STD),Residual (RES) and ARSTAN (ARS) chronologies. The STD chronology, which preserves more growth features, was applied in this study. Correlation analysis indicates that there is significantly positive correlation between tree-ring width standardized chronology (STD) and the average relative humidity of four meteorological stations (May-September) in the source region of Yellow River (r = 0.6, 1969~2013). Based on the analyses, the relative humidity sequence in May-September of Yellow River source region during 1505~2013 was reconstructed. The reconstructed equation was stable and reliable and its explain variance reached 36.0%. In the past 509 years,there were 6 wet periods (1655~1697, 1746~1793,1795~1816,1898~1916,1933~1957 and 1962~1992) and 8 dry periods (1530~1541, 1544~1586, 1590~1634,1728~1745,1817~1836,1856~1886, 1917~1932 and 1993~2004). The longest wet period is 1746~1793 (48 years),and the longest dry period is 1590~1634 (44 years). The wettest period is 1970s~1980s, and the driest period is 1600s ~ 1620s. There were 18 extremely dry years: 1510, 1513, 1536, 1605, 1606, 1607, 1608, 1609, 1617, 1618, 1626, 1627, 1824, 1831, 1871, 1895, 1927 and 1998; and 4 extremely wet years: 1773,1910,1975 and 1986. Comparison with the dry/wet events recorded in the history of the region from the yearly charts of dryness/wetness in northwest China for the last 500-year period shows many extreme years (wet years such as 1773 and 1986) and dry years (1510 and 1927) in the reconstruction. The multi-taper method (MTM) spectral analysis indicates that there are 3 periodic change of 85~256a, 3.0~3.6a and 2.0~2.8a. The 3.0~3.6a and 2.0-2.8a cycles may relate to the Quasi-biennial and Southern Oscillations influenced by alternating east-and west-wind regimes in the equatorial stratosphere lasting 26~30 months. By comparing the reconstructed sequence with the two reconstructed series which can reflect the status of dry and wet in the source region of Yangtze River and the northeastern Tibetan Plateau, it is found that these three areas share the same drought (1810s ~ 1830s,1870s ~ 1880s and 1920s~1930s) and wet periods (1750s~1760s,1890s~ 1910s, 1940s~1950s and 1970s~1990s) on an inter-annual scale. The result shows that these series have good consistency change on the low frequency. Compared with other tree-ring chronologies of nearby areas, we found that some dry periods, such as 1728 ~ 1745, 1817 ~ 1836, 1856~1886 and 1917~1932,coincide with low-growth periods of trees in these regions. Furthermore, we explore the climate mechanisms between the reconstruction and large-scale climate forcing.