Based on NCEP 2.5°×2.5°reanalysis data of wind and daily station precipitation data from 1998 to 2008,a regular pattern is found that when there is a heavy rain in Shanghai,10—20 day LFO zonal wind along 30°N in East China becomes stronger than normal and there is 10—20 day LFO southerly wind in Fujian and Zhejiang coastal area at the same time.So define the two areas as influencing areas.After doing lag correlation analysis with 10—20 day LFO wind in whole field and 10—20 day LFO zonal and meridional wind of the two influencing areas separately,two key areas are found,which are area 110°—130°E,0°—10°N and area 160°—140°W,45°—55°N respectively.It is found that 10—20 day LFO zonal wind propagates from area 110°—130°E,0°—10°N to the region around Shanghai and 10—20 day LFO meridional wind propagates from area 160°—140°W,45°—55°N to Shanghai.Therefore through LFO propagation,10—20 day LFO wind of the two key areas would influence the weather of Shanghai area.Results also show that 10—20 day LFO zonal wind and 10—20 day LFO meridional wind of the two key areas have a good relationship with precipitation of Shanghai 15—20 days later.Prediction test shows that the 10—20 day LFO wind in the two key areas can be good indicators of extended range forecast of summer precipitation in Shanghai.