Abstract: The study is intended to provide a basis for the ecological water demand, water supply and ecological sustainable development in the source area of the Yellow River, therefore, the ecological water demand of soil and water conservation is calculated by small watershed comparison method, and the driving factors of ecological water demand are analyzed by principal component analysis method, based on the data of soil and water loss area, annual evaporation and average annual temperature in the source area of the Yellow River from 1990 to 2020. The results show that the area of soil and water loss caused by soil erosion in the source region of the Yellow River showed a decreasing trend from 2005 to 2020, and the area of soil and water loss in 2020 declined by 43.58% compared with that in 2005. From 1990 to 2020, the ecological water demand for soil and water conservation in the source area of the Yellow River increased by 2.6×10⁶ m³; in the principal component analysis, the contribution rates of factor with eigenvalue greater than 1 were respectively 75.689%, 11.783% and 7.767%; and the cumulative contribution rate reached 95.239%. To sum up, social and economic development is the main driving force of the total ecological water demand change in the source area.