Using the Micaps regular date,correlation and statistical analyses between sandstorm days and the upper level jet stream between 30～50°N during 2000—2004 are carried out in this study.The results show that the sandstorms accompanied by the upper level jets can be divided into 2 kinds:single jet stream pattern and double jet stream pattern.For single upper level jet patterns,sandstorm is likely to occur beneath the left side and right rear side of the upper level SW or NW jet stream;and for double(a NW plus a SW) jet streams patterns,sandstorm is likely to takes place beneath the left front side of the NW jet and the left rear side of the SW jet,or beneath the right front side of the NW jet and the left rear side of the SW jet.Dynamic analyses on the vertical distributions of wind filed structure and the vertical structure of circulation field for selected typical sandstorm cases are also carried out.The analysis results suggest that the upper level jet associated with sandstorms includes single jet pattern,double jet pattern and even trijet pattern;generally the height of the north branch upper level jet is lower,at 300 hPa,and the south branch jet is higher,at 200 hPa;the maximum wind speed of the south branch is greater than that of the north branch;the north branch jet tilts to the south with height,while the south branch leans northwards with height.Sandstorms for single jet pattern mostly occur beneath the south side of the descending leg of the secondary circulation of the north branch jet,and sandstorms for double jet pattern are likely to occur beneath the merged descending leg of the two jets,sandstorms could occur either in the desceing area of upper level jet or in the ascending area:in the ascending area,the suction resulted from the low level convegence and the upper level divergence induces the low level strong winds and sandstorms,and in the descending area,the downward transfer of upper level momentum is in favor of the genesis of sandstorm.Between the north and south branch jet streams there always is a vertical circulation cell,which facilitates the genesis of sandstorm,therefore both the north branch jet and the south branch jet jointly impact the genesis and development of surface sandstorms.