Abstract: It is of great significance for drought monitoring and water resources management to study the evolution of hydrological drought under the effect of reservoir runoff regulation. Based on the monthly measured runoff data from 1956 to 2020 at Huangjiagang and Huangzhuang stations in the middle reaches of Hanjiang River, the standardized runoff index(SRI) was used to analyse the hydrological drought changes before and after the Danjiangkou(DJK) Reservoir impoundment. The variations of joint probability and return period of hydrological drought characteristic variables were evaluated based on Copula function. Results indicated that:(1) Compared with that before the DJK Reservoir impoundment, the drought situations in winter at the two hydrological stations after operation of the DJK Reservoir were significantly reduced, while the drought conditions in summer and autumn were slightly aggravated, especially at Huangjiagang station;(2) After the impoundment of the DJK Reservoir, the frequency of light drought events at Huangjiagang station increased significantly, and that in Huangzhuang station increased slightly, while the frequency of moderate, severe and extreme drought events at the two hydrological stations decreased significantly;(3) As for the average value of drought duration and severity, Huangjiagang station increased and Huangzhuang station decreased slightly after operation of the DJK Reservoir. From the average value of drought peak, the two hydrological stations decreased in varying degrees after impoundment of the DJK Reservoir;(4) Given a certain return period, the joint return period of drought characteristic variables of the two hydrological stations after impoundment showed an increasing trend, while the co-occurrence return period exhibited a downward trend as a whole;(5) In dry years, increasing the outflow of the DJK Reservoir can alleviate winter and spring drought conditions in the middle-lower reaches of Hanjiang River to some extent, but the impoundment of the reservoir at the end of the flood season reduces the streamflow of the downstream river, which may aggravate the drought condition.