Abstract: Moisture budgets during heavy rainfall events in the Huai River Basin from June 29 to July 11 of the 2003 Meiyu season are studied by using the ERA Interim reanalysis data and rain gauge records. It is shown that the water supply to the rainfall is mainly from the low-level convergence of moisture. The moisture convergence associated with the low-level jet has a remarkable diurnal variation with a maximumduring midnight to early morning and an afternoon minimum, which produces a characteristc precipitation diurnal cycle during the Meiyu season. The evaporation mainly concentrates in the daytime and constitutes about 15% of the amount of precipitation, indicating the importance of the regional moisture recycling. Over the Huai River Basin, the left and right sides of the moisture budget equation have a good consistency with a correlation coefficient of 0.77 throughout the 2003 Meiyu season. When averaged over time, a moisture imbalance of 18% is obtained.