Water is the most important resource in the world for the survival of living things and it is the most essential resource associated with changes in land use/ land cover. The main objective of this study was to evaluate the impact of land use/ land cover changes on the stream flow of upper guder catchment. Specifically, the study analyzed land covers that have taken place in the catchment and its effect on the stream flow. Land use/cover change scenarios were used to determine the potential impacts that would happen on the catchment stream flow. The Soil and Water Assessment Tool (SWAT-2012) model was used to investigate the impact of land cover change on stream flow of the study area. The model was set up using readily available spatial and temporal data, and calibrated against measured discharge and the land use/land cover change analyses were performed using ERDAS Imagine 2014. Land use/cover changes for three different years of 1987, 2001 and 2018 land use/cover scenarios were used for estimation of stream flow. Sensitive parameters that used to calibrate the model were SCN curve number (CN), Ground water delay (GW-DELAY), Threshold water depth in the shallow aquifer for flow (GWQMN), Surface run off lag coefficients (SURLAG), Threshold depth of water in the shallow aquifer (REVAPMN) and Soil Available Water Capacity (SOL_AWC), were found the most influential parameters affecting flow.The performance of the model was evaluated on the basis of performance rating criteria, graphical method, water balance, coefficient of determination (R2) and Nash Sutcliff efficiency (NSE). The R2 and NSE values for the catchment were (0.715 and 0.78) for flow calibration, (0.714 and 0.83) for flow validation in daily basis, (0.884 and 0.812) for flow calibration, (0.838 and 0.823) for flow validation in monthly basis respectively. The result of this analysis indicated that the mean monthly stream flow was increased by 12.54m3/s for the wet months while for the dry months was decreased by 0.65 m3/s. In general, from the result of land use scenario, the changes in stream flow characteristics could be related to the change of the land use. The SURQ increased, while GWQ decreased from 1987 to 2018 due to the increment of cultivated lands due to population growth. The model results showed that the stream flow characteristics changed due to the land cover changes during the study period. The performance of the model can be improved by increasing the number of rainfall and discharge gauging stations within the catchment.