Seasonal drought is the most prominent meteorological disaster which affects spring maize production in Hunan Province. Therefore, analyzing its temporal and spatial distribution characteristics and occurring rules are important to provide technical supports for the development and reasonable layout of maize production in Hunan Province. Weather data of 96 stations from 1961 to 2007 were used to calculate the reference crop evapotranspiration (ET0) and crop water requirement (ETc) of maize by the method of Penman-Monteith formula commended by FAO(1998). In this paper, effects of surplus water on crop water deficit index (CWDI) were considered, and the calculating method of CWDI was modified. The frequencies of different classes of drought were calculated and their temporal and spatial distribution characteristics were analyzed by the modified method of CWDI subsequently. Typical stations in different regions were selected to analyze the inter-decade variations of modified CWDI. Results indicated there were significant seasonal and spatial distribution characteristics. Drought occurred in high frequency at the stage of tasselling to silking and thereafter. Drought frequency obviously increased with backwards shift of growth stage. Light drought happened in higher frequency than medium and severe drought. In space, drought occurred with the highest frequency in Hengyang and its surrounding area in mid-south part of Hunan, followed with the east and north part, and low frequency region located in west part. Drought was more serious in 1980s, and became light in 1990s.