In this paper, the most suitable summer monsoon index is selected to determine the summer monsoon year in the Huanghuai region. Combining with the summer daily precipitation data in recent 55 years, the difference of summer rainfall between strong and weak years and the formation causes are discussed. The main conclusions are as follows： In the strong summer monsoon year, the precipitation in the east is more than that in the west, and in the weak summer monsoon year, on the contrary. Before 1979, the precipitation in the region had a cyclic interannual variation with the periods being 3 to 5 years, but after 1979, the period evolved to 15 years. At the same time, the regional precipitation was characterized by low frequency oscillation. In the strong summer monsoon years, there were 7 to 14day oscillations and two rainy seasons which occurred in early July and late August, respectively; in the weak summer monsoon years, the low frequency oscillations of 10 to 18 day and 25 to 30 days were remarkable, but the main rainy season was not obvious, and precipitation was less. The differences of annual precipitation between strong and weak summer monsoon years are mainly attributed to the different wave trains of the largescale circulation background in the midhigh latitudes of the Eurasia and the difference of water vapor transport in the southerly monsoon. The spring SST anomaly can indicate the precipitation in the Huanghuai region. In La Nina years, the precipitation in the eastern part of the Huanghuai area was more than that in the western part, and in the El Nino years, on the contrary.