Abstract This study aimed at investigating the applicability of a SWAT (Soil and Water Assessment Tool) model in understanding the effects of drought on summer maize. A real-time irrigation module was developed for the downstream irrigation area of the Yellow River to estimate the real-time irrigation of crops. By further simulating the dynamic evolution process of soil moisture content, a dynamic drought evaluation model of summer maize was established, and the relative soil moisture was set as the evaluation index to assess and analyze the dynamic variation of drought evolution during the growth of summer maize. The results showed that the improved SWAT model has strong applicability. During the growth of summer maize, the variation trend of drought is consistent with that of natural precipitation. Moreover, drought mainly occurs during the sowing-seedling and seedling-jointing stages, and the average frequency is 84.8 and 78.3%, respectively. Moderate drought is most likely to occur during the growth of summer maize and occurs mainly during the sowing-seedling and seedling-jointing stages, and the occurrence frequency is 55.3 and 32.6%, respectively. Extra-severe drought has the greatest impact, mainly in the jointing-tasseling, tasseling-milking and milking-maturity stages, and the occurrence frequency is 17.4, 15.2 and 10.9%, respectively.