Water discharge is valuable information for strategies on exploitation management, erosion control, determination of flow trends, flood forecasting, and assessing the impact of climate change on water flows. Hydrological models were developed in response to the need for tractable techniques that could simplify the relationships between rainfall and runoff. The runoff curve number so called a curve number is an empirical parameter used for forecasting and quantifying runoff. This study aims to estimate the curve number index based on remote sensing and GIS (geographic information system) in the Vu Gia - Thu Bon river basin.