Using the Empirical Orthogonal Function (EOF), correlation and composition analysis, the interannual and interdecadal variability of the 500-hPa zonal wind in summer in the Tibetan Plateau and its relationship to the precipitation in China are examined, based on the monthly NCAR/NCEP reanalysis data and the precipitation data from 160 stations in China. The results of spatial-temporal structure reveal that: in general, 500-hPa zonal wind in summer in the Tibetan Plateau shows a decreasing trend since 1950. And the westerly wind was weaker in the 1950s and stronger significantly in the 1960s. From the 1970s to the early 21st century the westerly wind has been in a weak phase. The spatial distribution of zonal wind trends reveals that most of the zonal wind over the plateau region show weakening trend and the trend decreases from southeast to northwest, and the most decreasing trend takes place in the northwest and the middle of the plateau. The first EOF mode of the 500-hPa zonal wind shows that the decreasing trend takes place in the whole region, and its time coefficient shows the long-term positive trend. The 11-year moving average of time coefficient shows that the increasing trend of the zonal wind taking place in the whole region was more obvious from the late 1950s to the late 60s, and from the late 1960s to the early 21st century the westerly wind has been in a weak phase and has no significant increase or decrease. Mutation analysis of the time coefficient shows that there was a pronounced weakening mutation of the zonal wind in 1967. Wavelet analysis of time coefficients indicates that it has the cycle of 2－4 years and the cycle component is more significant in the early 1950s and from the late 1990s to the early 21st century. The relationships between interannual and interdecadal weakening of the 500-hPa zonal wind in summer in the Tibetan Plateau and the precipitation in China is explored: when the zonal wind decreases, less precipitation happens in the north of the middle and lower reaches of the Yangtze River, especially in northeastern and northern China; much precipitation happens in the south of the middle and lower reaches of the Yangtze River. Meanwhile, relatively significant relationships are found between precipitation and circulation, divergence of water vapor flux.