Abstract: To analyze the water surplus and deficiency in the summer corns’key period in the Huaihe Basin for providing a reference for authority's decision-making and field management and agricultural production, the characteristic of water surplus and deficit was analyzed by water surplus deficit index based on meteorological data from 121 sites during 1971-2010 in the Huaihe Basin. The results showed that there was an obvious downward trend of water requirement to summer corns’key period, and the descending rate in the south was faster than that in the north, while the rate in plaint was faster than that in mountain area. The annual average water requirement to summer corns’key period showed a clear characteristic that there was an increasing trend from north to south in the zonal space distribution. It was characterized that the precipitation of annual average water requirement in the south and plaint was greater than that in the north and mountain area, while with no significant increase on the precipitation during summer corns’key period. The effective precipitation was in conformity with that in spatial distribution. The average water surplus deficit index of each region showed a water deficit, but the tendency of yearly variation was increasing. The spatial distribution of the annual average water surplus deficit showed an increasing trend from south to north. The water deficit was much serious in the northern plain area.