It is of great significance to find the precursory signals and establish a forecasting mechanism of drought and flood for the Huaihe River Basin due to the frequent drought and flood. Based on the precipitation data of the Huaihe River Basin, the sea surface temperature (SST) of North Pacific and the geopotential height of 500 hPa in Eurasian continent from 1968 to 2017, the improved Z-index method was used to assess the grade of summer drought and flood in the Huaihe River Basin in the past 50 years. The precursory signals from SST and geopotential height of 500 hPa that can affect precipitation were found. A mathematical model has been established for forecasting summer drought and flood index values in the Huaihe River Basin. The results showed that the drought and flood in the Huaihe River Basin were severe. The drought had a weak downward trend, but the flood was reversed. The key areas of the SST signal were located in the Thousand Islands, the Philippine Sea to the Central Pacific and the Nino4 district. The key areas of the 500 hPa height field are distributed in the east of the Siberian Mountains, the Eastern European and Western Siberian plains, and the West Asia region. The equations established by the stepwise regression method had good forecasting accuracy and practicability, and can predict the drought and flood index of summer precipitation in the Huaihe River Basin. It also can be used for monitoring and forecasting drought and flood in the basin.