Problems in providing satisfactory water supply to the rapidly growing population especially that of the developing countries is increasing from time to time. The adequate and reliable water supply in Ethiopian towns is becoming a challenge for most water utilities. Hence, this study was conducted to carry out the hydraulic performance evaluation of water distribution system of Aiyteyef subsystem in Dessie town using statistical analysis and WaterGEMS software. A statistical analysis was applied to analyze the current water supply coverage and total water loss of the entire town. Accordingly, to examine the hydraulic performance of the water distribution network, WaterGEMS modeling was adopted. It was performed by considering the system as continuous water supply system, and the evaluation and modification process adopted the Extended Period Simulation method. To reduce the difference between measured and predicted flow and pressure, calibration was performed using the most sensitive parameter, which is pipe roughness. From the result of the analysis, it was observed that the total water loss of the subsystem is high reaches up to 35.4 % of the system input volume and about 16.7% of the total system loss is unavoidable real loss due to high-pressure impact. Besides, the average daily per capita water consumption of the town is 27.4 liter/person/day and average level of connection per family is 41%. Hence, this result indicates that there is high gap between demand and supply. The calibration result provided the roughness value of 126 for the PVC, 100 DI and 90 for the GI pipe with the overall average root mean square error of 1.19m, which indicated good model performance. After calibration, Simulation results for maximum and minimum nodal pressures, flow velocity and tank level were used as base parameter to analyze and improve the hydraulic network of the system. The analysis result showed that there were various problems in the system. Which are oversized pipe related to the currently available existing source, 6% and 12% of the junctions were below and above the allowable limit (15 to 80 mH2O) of pressure at peak hour demand, tank level empty due to over level of needed demand than the available demand in extended period simulation. The system should be modified using the design criteria of velocity and pressure. High pressures in the existing system caused by low level of elevation relative to the service reservoir had been identified and solution is established using pressure-reducing valves and removed unnecessary looped system. The existing piped network is enough to accommodate the needed demand. So, securing additional water source should be need to solve low velocity impacts and to improve the current situation of the case study water distribution system.