The watershed Garonne is important in hydrologic systems responsible for much of the water supply in the area of Haute-Garonne. The watershed is increasingly facing anthroprogenic and climate related pressures that impact spatial and temporal distribution of water availability. This study evaluates the temporal and spatial distribution of water quality including nitrate concentration. The water movement, calibration of the sediment and the nitrogen cycle of the Garonne river basin are simulated using the hydrological modeling software SWAT (Soil and Water Assessment Tool). The main objective in this project is to model the flow of water and to calibrate the suspended sediment (SS) and nitrate transfer in the river continuum within the watershed of the Garonne river in order to simulate over a long period at daily time scale. The model assessment showed that SWAT is able to simulate water, suspended sediment and the movement of nitrate in the region with satisfactory results.