Abstract: Analysis of the moderate or heavier precipitation process and atmospheric intraseasonal oscillation showed that an obvious dipole of intraseasonal relative vorticity exists during the rainy days. According to the dipole,a pair of intraseasonal indices for forecasting is created,as well as the forecasting method with the indices. With the indices,both tests of forecasting historical precipitation processes and an experiment for forecasting precipitation process in the summer of 2014 are made. The results indicate that the intraseasonal method for extended range forecast is quite capable of forecasting the moderate or heavier precipitation process over the lower reaches of Haihe River,which can be used in actual extended range forecast service.