It's mandatory to assess the hydraulic performance of water supply distribution systems to address water distribution issues in an urban water supply system. This can be accomplished by analyzing the current status of the water distribution system. This study was aimed to analyze the existing water distribution system in kombolcha town using WaterGEMS (Geospatial Engineering modeling software) software. WaterGEMS model was used for automated calibration and analyzing the hydraulic parameters of water distribution system. To reduce the difference between measured and predicted pressure, the model was calibrated at the selected nodes within good performance. The result showed that the water supply coverage was low which covers only 69.4%. besides water demand and supply of kombolcha town were not balanced. The people used daily water of 50 l/day with the billed water amount is 67.1% of production and 32.9% water is considered to be non-revenue (NRW). The simulation result of the existing water distribution system showed that, during peak hour demand 23.1% of junction have low pressure (<15m H2O) and during minimum demand hour 67.4% of the junctions have high pressure (>60m H2O). The hydraulic performance analysis also revealed that 83.5% and 24% of total pipes have velocity below 0.6m/s at minimum and peak demand respectively. The study concluded that the hydraulic performance of Kombolcha town water supply distribution system is running below the expected level. Thus, the high pressures in the distribution should be managed by using pressure reducing valves and a low pressure and velocity should be improved by making rehabilitation of existing boreholes, which satisfy the existing peak water demand in the town. Keywords: Hydraulic performance, WaterGEMS, Darwin Calibrator, Water loss