This study evaluated the Soil and Water Assessment Tool (SWAT) model performance for modeling the portioning of rainfall in the Laou watershed (area: 940 km2) that extended over two different climatic settings in Morocco, (the Mediterranean sub-humid and the semi-arid). This research also investigated the significant parameters that affect the stream flow simulation. SWAT model was constructed during the period from 2004 to 2011. The modeled stream flow data was manually calibrated using flow gauges daily from 2004 to 2008 and validated for the volumetric flows from 2009 to 2011. SWAT model results indicate that 60% of the stream is provided by the base flow. The sensitivity analysis showed that out of 28 parameters, only 6 revealed meaningful effects on the flow simulation (CN2, ESCO, SOL_AWC, ALPHA_BF, CH_N2, CH_k2) and have the most significant influence. The model proved to be very sensitive to the base flow. Furthermore our outcome indicates that SWAT can successfully replicate the daily stream flows in Laou watershed with Nash-Sutcliffe (NSE) coefficients in the range of 0.76-0.84, R2 of 0.74-0.82, RSR of 0.52-0.41 and PBIS of 12.24-8.93 respectively. In addition SWAT was found to be suitable for both climatic regions in Laou watershed. These results reinforced the multi-functionality and reliability of SWAT as a hydrological model and a relevant tool for water resources management and controls.