With the aid of the NCEP/NCAR monthly reanalysis data-set and the summer precipitation data in the east of northwest China during 1951-2002,the interannual variability of cross-equatorial flow and its influences on summer precipitation in the east of northwest China are analyzed.It is concluded that the cross-equatorial flow has strengthened and is more persistent since 1951;and the Somali jet is the principle and stable cross-equatorial flow,and also an important circulation factor which affects the summer precipitation in the east of northwest China.