Analysing the hydrological regime of watersheds and driving factors is important for understanding hydrological processes. This study used hydrological data from 1986 to 2018 from the Luoyugou (LYG) watershed to quantitatively analyse the hydrological regime and contribution rates of driving factors using the range of variability approach (RVA) and the Soil and Water Assessment Tool (SWAT) model, Budyko and two empirical methods. The results show that: (1) The degree of hydrological alteration (DHA) for most ecologically relevant hydrologic indicators (ERHIs) was 68.16% and 69.13%, indicating a high degree of alteration. The hydrological regime and river ecosystem have undergone significant changes. (2) Under the influence of human activities, the flood sediment load decreased by 66.74% and the flood sediment-carrying capacity increased significantly. (3) Large-scale human activities, such as land use/cover change (LUCC) and soil and water conservation measures (SWCMs), are the dominant factors causing changes in the hydrological regime. The SWAT model and double mass curve (DMC) method have higher accuracy of the contribution rate than Budyko and the linear regression model (LRM) method, as the latter two have limitations that may lead to an underestimation of contributions. This study can serve as a reference for assessing hydrological regimes and the impacts of ecological restoration in other regions worldwide.