Hydrologic models have been used in different river basins across the world for better understanding of the hydrological cycle and the water resources availability. It is necessary to apply hydrological models, know adays to evaluate and estimate the water availability of river basins. However, proper model implementation will require for verification of the model against known output parameters. This study investigated the performance and applicability of hydraulic engineering center hydrologic modeling system (HEC-HMS) on Borkena catchment by using HEC-HMS version 4.8 in range of watershed sizes (228.11km 2 ) in the Awash Basin to estimate peak flood, time to peak, run off volume, and evaluate the model performances. The simulation model was based on the watershed and its surface characteristics of the soil, land use land cover and elevation of the area. 14years meteorological and hydrological data were used for model calibration and validation. Model Calibration were carried out using the observed and the simulated stream flow data from 1989-1997 and a validation period from 1998-2002. Multi-objective function statistics: Nash–Sutcliffe Efficiency (0.65, 0.704), Root Mean Square Error (RMSE) (0.6, 0.5), Coefficient of Determination, R 2 (0.693, 0.713), and Percent Bias, PBIAS (12.84%, 12.16%) for calibration and validation, respectively were obtained. The observed peak stream flow for calibration and validation was 165.3 m 3 /sec and 197.3m 3 /sec but from the simulated result the simulated peak flow for calibration and validation was 122.6 m 3 /s and 155.2 m 3 /s respectively. As we see from observed and simulated flow that HEC-HMS sightly under-predicted peak flow and runoff volume in both calibration and validation periods. However, according to a daily and weekly time step model Statistical evaluation guidelines and performance ratings, modeled peak discharges and obtain runoff can be rated as satisfactory and acceptable accuracy. The major advantage of employing a GIS-based approach in rainfall-runoff modelling is the use of different land use patterns, soil data especially in regions with a complex mix of land use features (urban and cultivated area) and different soil types. Better spatial and temporal resolution of rainfall data is required to further improve the model performance and to further enhance the understanding of the runoff processes in the catchment area. Keywords: Borkena watershed, Flow Simulation, HEC-HMS, Hydrograph and Peak Flow