In a changing environment,the drought index may appear the non-stationary characteristic.In this study,we assuming that the runoff series are second-order non-stationary sequences,a non-stationary model was established and optimized to fit the runoff observations and was used to calculate the Time-dependent Standardized Runoff Index(SRIt)that could reflect the drought characteristics in a river basin.The results show that SRIt based on the non-stationary model is more suitable for the evaluation of hydrological drought in the changing environment of Panjiakou Reservoir watershed.The SRIt value calculated by the non-stationary model is generally smaller than SRI value that calculated by the stationary model,which represents the more seriously drought degree.The main reason is that time-varying moment model can reflect the trend of runoff series under changing environment,which is caused by a series of factors affecting runoff,such as climate change,human activities and so on.Under the influence of these factors,the frequency and severity of hydrological drought events in Panjiakou reservoir basin increased.