This paper presents an interpretation method of blending dynamical and statistical approaches for ensemble prediction products,which establishes the prediction equations for dekad precipitation anomaly by deriving the relation between the dekad rainfall anomaly and potential height anomaly based on atmospheric dynamics equations,two-layer baroclinic model and the characteristic of medium-range dekad-scale atmospheric circulation.Comparing it with the equivalent-barotropic rainfall anomalous percentage equation the baroclinic one fits much more to the situation of real atmosphere in the low and middle latitudes.The results of experimental forecasting show that the method of blending dynamical and statistical approaches is useful for forecasting dekad rainfall anomaly by using potential height of Ensemble Prediction System(EPS).