Abstract: Based on the data of daily temperature and precipitation in spring maize growth stages collected from 15 observation meteorological stations in Shanxi province from 1981 to 2011, relative moist index(M) in different spring maize growth stages were calculated, and combined with coupling degree between precipitation and spring maize water requirement, the variability of drought of recent 31 years in growth stages of spring maize in Shanxi province were analyzed. The results indicated that，(1) in recent 31 years, the highest drought frequency of 86.95% occurred in seeding to jointing stage of spring maize in Shanxi province, in which there was most serious water scarcity, and the coupling degree between precipitation and spring maize water requirement was only 0.41, which was the lowest during the spring maize growth stage, and most of the droughts were moderate drought, strong drought and severe drought; In sowing to seeding stage of spring maize, the drought frequency was 82.47%, and most of the droughts were moderate drought, strong drought and severe drought, the coupling degree between precipitation and spring maize water requirement in northern and middle part was 0.45 and 0.41 respectively, but the precipitation was matched with the spring maize water requirement in southern Shanxi. In jointing to tasseling stage of spring maize, the coupling degree between the precipitation and spring maize water requirement was 0.69, the drought occurrence frequency was 51.51%, and most of the droughts were slight; the drought occurrence frequency was 32.58%-43.33% in tasseling to milky maturity and milky maturity to full maturity stage of spring maize, in which most of the drought was slight drought, and precipitation was generally matched with the spring maize water requirement. (2)Drought occurrence frequency was decreased and coupling degree between precipitation and spring maize water requirement was increased from Northern to Southern Shanxi. The proportion of moderate, severe and extra severe drought occurrence frequency to all the drought occurrence frequency were highest in sowing to seeding of spring maize, which was up to 86.73%,79.43% and 72.88% in Northern, Middle and Southern Shanxi, respectively.

Key words: Spring maize, Growth stage, Drought occurrence frequency, Relative moist index, Coupling degree