Abstract: Impacted by climate change and human activity， catchment scale environment has changed and leaded to remarkable runoff variation， which poses a new challenge to water resources management. Attributing and defining the climate change and the human activity impacts on catchment runoff could scientifically support the measures and actions of environmental change mitigation and adaptation， which is also one of the urgent key problems in sustainable water resources management. In current studies， the hydrological model-based methods indicate averaging effect and additive error above annual scale， and are normally complicated with more uncertainties due to excessive parameters. Based on Budyko hypothesis， this study has presented an attribution method to assess catchment scale runoff variation impacted by the climate change and the human activity. The Sanchuan River basin in Loess Plateau is selected as a case study. The analysis results show that the proposed method has a preferable applicability to runoff variation analysis for annual scale， compared with the application from VIC model. Because there are no true values of separated impacts from the climate change and the human activity， this method enriches the research theory for the issues， and facilitates the understanding of the impact of the regional environmental change.