Due to the importance of analyzing the hydrological behavior of basin, especially basins with no hydrometric station, applying new methods for predicting water balance is necessary. Therefore, in this research daily runoff stream of Gamasiab basin in the south of Hamadan and Kermanshah provinces was simulated based on cellular network using hydrological spatially distributed WetSpa model in GIS. Digital maps of DEM, land use and soil texture and continuous time series of temperature, precipitation, evapotranspiration and discharge are main model inputs. Model in any cellular network by using rainfall, temperature and evaporation data, simulates all water balance components. Calibration of model parameters for the last 20 years of the studied period (1991 to 2010) and validation of model for the first 5 years (1986 to 1990) was done. The results of the model application showed good agreement between observed and simulated data based on statistical criteria of Nash- Sutcliffe efficiency criterion with accuracy above 0.6 .This model based on the coefficient of performance showed that ability to simulate rainfall-runoff in major sub basins is satisfactory.