The upstream side of the large watersheds of Benin is undergoing accelerated degradation phenomena, due to human pressure. The objective of this study is to quantify the loss of cultivable soil in the Affon-Donga watershed. The methodological approach adopted was to use the RUSLE model to quantify soil loss. Raster data such as SoilGrids images from ISRIC, elevation images from ASTER GDEM, Landsat OLI images, WoldClim data as well as terrain data were used to prepare the five factors of the model. The results obtained show that the soil loss varies between 0 and 21,598.63 t / ha / year in the Affon-Donga watershed. The loss values ​​of between 10 and 500 t / ha / year occupy 40.54% of the basin. The colossal losses which exceed 500 t / ha / year and go up to 21,598.62 t / ha / year are dispersed over 3.95% of the basin. The average soil loss is 1443.81 t / ha / year and the rate of erosion or the amount of soil moved generally from upstream to downstream is 633,562,753.72 t / year. As the long-term result of such an ecosystem dynamic, cultivable spaces will become scarce while the processes of filling and meandering of downstream rivers will be amplified.