Abstract: In order to provide evidence to precipitation prediction in Shaanxi province,the impacts of Western Pacific Subtropical High (WPSH) in mid summer on precipitation in Shaanxi province and its mechanism was analyzed by using of correlation analysis,regression analysis and wavelet coherence spectra analysis,based on precipitation data collected from 78 meteorological stations in Shaanxi province, monthly WPSH indices data provided, monthly reanalysis datasets about 500hPa geopotential height and 700hPa wind field from July to August from 1961 to 2008.The results showed that there was correlation among precipitation and the intensity,ridgeline location,western extension ridge point of the WPSH.The rainfall was more than normal when WPSH was strong and further west,when WPSH was located further north than normal，precipitation was more than normal in northern Shaanxi and less in southwestern.The three indices of WPSH in August had more close relationship with precipitation,and the numbers of stations which passed significance test were obviously increased.Anomalous atmospheric circulation in subtropics and mid high latitudes was caused by the intensity and location variation of WPSH,which influenced precipitation in Shaanxi province further more.When WPSH was stronger and further west,the Balkhash Lake Block and 700hPa summer monsoon strengthened,Shaanxi province was located the confluence of cold and warm air,and precipitation would be higher.However,when the WPSH moved toward south,water vapor convergence zone located in southern Shaanxi,and vice versa.There was a remarkable resonance cycle of 7-8 years between the high intensity index of WPSH and precipitation in Shaanxi in August,and the intensity index of WPSH ahead of the precipitation changes 1.26 years,which indicated that annual precipitation variation in Shaanxi mainly caused by WPSH annual intensity variation.

Key words: Western Pacific Subtropical High index, Mid summer precipitation in Shaanxi province, Wavelet coherence spectra, Resonance cycle