In Morocco, although it is often classified as a country with a semi-arid climate, floods are very frequent. Like other basins in the kingdom, the Sebou basin with a total area of 40 000 km² has experienced more catastrophic flooding in the past and these floods have caused enormous economic and even human losses. The objective of this study is to apply different methods to calculate a Curve Number values to estimate the potential runoff for this basin. The techniques used are boils down to the different steps. Firstly, the approach was to extract automatically the sub-basins and drainage network, using Geographical Information Systems (GIS) and Digital Elevation Model (DEM) to determine all the physical characteristics of the basin. Then, preparing the land use map using remote sensing and the soil map for determining hydrologic soil Group. Thirdly, the combination of elaborated data for development of a map of Curve Number (CN) and finally, the interpolation of precipitation data recorded at rainfall stations at 30 minutes time steps to the Hydrologic Modeling System (HEC-HMS ) model. The results obtained in the above steps are used for the purpose to get a spatial hydrological model and subsequently its calibration.