Storm water drainage problem is one of the major challenges facing in Dagmawi minilik sub city, Bahir Dar. The study focuses on the hydraulic performance of the existing drainage systems in Dagmawi minilik sub city, Bahir Dar. Maximum annual rainfall data from 1992 to 2021 were used. The intensity duration frequency curves of the study area was developed using Log Pearson type-III method. The physical parameters catchment delineation; dividing the catchment into sub-catchments and parameterizing the required elements for the model were examined using Google Earth. There are 34 sub-catchments make up the model's area, and its drainage system consists of 42 channels, 42 junctions, and 2 outfalls. To determine the culvert catchment peak discharge and culvert flow overtopping has been performed using civil 3D. The maximum channel flow rate, maximum velocity, and maximum water level observed were assessed using floating method and calibrate with SWMM model. R Studio has been utilized to more calibrate the model. The Model Performance Evaluation of Dagmawi Minilik sub city was assessed using the coefficient of determination r 2 and Nash-Sutcliffe efficiency NSE. The calibration resulted in r 2 of 0.88 and NSE of 0.84, validation resulted in r 2 of 0.91 and NSE of 0.89. The calibration and validation results indicated a good fit between simulated and measured data. Total runoff from the whole sub catchments is 96.25m 3 /sec using Rational Formula whereas from the same catchment using SWMM model is 102.8m 3 /sec. The simulation results of 10 year return period design rainfall show that maximum flooding occurs at some channels C4, C8, C9, C10, C18, C19, C20, C23, C25, C31, C32, C37 and C39, were occur channel surcharge and all Nodes were arise flooding. Overflowing junctions J2, J4, J6, J7, J11, J10, J15, J20, J22, J25, J26, J30, J31, J32 and J33 are nodes flooded. The simulation result of 25 years return period design for culverts (1, 2, 3 & 4) has overtopping problems. . Keywords: SWMM, Calibration, Validation, R Studio, Urban drainage, civil 3D