The spatially distributed hydrologic model WetSpa is applied to the Dinvar river basin (1717 km²) located in upstream of the Karkheh Dam. Daily hydrometeorological data from 1382 to 1389, including precipitation data from 9 stations, temperature and evaporation data measured at 4 stations are used as input to the model. The spatial characteristic of the basin is described by three base maps, i.e. DEM, land use and soil type, in GIS form using 100 m cell size. Results of the simulations show a good agreement between calculated and measured hydrographs at the outlet of the basin. The model predicts the daily discharge values with a good accuracy, i.e. about 66% according to the Nash-Sutcliff criterion. Sensitivity and uncertainty analysis of the model parameters is performed using a model-independent parameter estimator, PEST. It is found that the correction factor for calculating the groundwater flow recession coefficient has the highest relative sensitivity and the parameters kss and kep located in two and three ranks of the relative sensitivity. Parameter uncertainty analysis shows that parameters ki; kep, kss and kg have high certainty and as well as parameters krain, kmax have low certainty.