With the Mann-Kendall and Morlet wavelet nonparametric test, the time-series of annual mean air temperature, precipitation and relative humidity (1957-2012) at Wudaoliang Station in Qinghai-Tibet Plateau were analyzed in order to find their changing tendencies. Meanwhile, based on R/S method, the changing tendencies in the coming period were also forecasted for the Wudaoliang area and it was found that temperature and precipitation had significantly increased in the past 56 a with a cycle of 30 a/18~19 a/10 a/5 a and 20~30 a/14 a/8~9 a; On the other hand, the relative humidity had decreased significantly with a cycle of 30 a/5 a/15 a. The forecast indicated that temperature and precipitation would increase but relative humidity would not decrease as had happened in the past. On the contrary, it may increase or become flat at a certain period of time after 2012 in Wudaoliang.