A precipitation index is designed and calculated, selecting such factors to be ingredients of IngredientsBased Forecasting Methodology as the divergence of nongeostrophic wet 〖WTHX〗Q〖WTBZ〗vector, MPV, and total volume water vapor. It is found that the precipitation index is in good agreement with real precipitation in value and trends. The precipitation index can reflect the wet and dry periods. With the NCEP CFSv2 data of April to June 2014, the precipitation index is calculated. The monthly precipitation index value can well reflect the maximum rainfall in May (usually in June). Ingredient method can provide a useful reference for shortterm climate prediction.