Using the data of 500 hPa heights over the Northern Hemisphere, North Pacific SST, atmospheric circulation, precipitation, etc. (1951 to 2009), the effects of various factors on the precipitation tendency in October 2009 are analyzed by using the methods of correlation analysis, composite analysis, EOF, wavelet analysis, etc. The results show that there are three distribution patterns of precipitation in Shandong in October 2009 Shandong is generally in the raindeficient period or the transition period from raindeficient to plentiful rainfall at various time scales. All the indicators, such as the weakening of the California cold flow in spring of 2009, El Nino starting from June 2009, and the strengthened, consistently farther west than normal，normal,farther south than normal West Pacific Subtropical high, show that the precipitation in October in Shandong will be less than normal, which accords basically with the observation.