Flood Hydrograph simulation is an essential step in analyzing the impacts of extreme flood events. This can aid in water resources management and planning. In areas that are prone to floods, it become necessary to perform an extensive hydrological study. North Koel subbasin is one of the flood prone watershed, mainly due to the confluence of two large rivers ‘Auranga’ and Amanat, in eastern side of catchment. This study mainly focused on simulation of flood hydrographs based on Global Curve Number Grid data with 250 m resolution (GCN250m) of 3 different Antecedent Runoff Conditions (ARC) using HEC-HMS model. In this study, hydrograph simulation was done using 3 types of ARCs Grid data namely ARC-I (named Dry condition), ARC-II (noted as Average condition) and ARC-III (Wet condition). Curve Number is one of the vital input parameter for runoff volume computation based on SCS-CN method, the direct runoff computed based on SCS-UH method. Also, Muskingum method used for routing of flood through reaches. The HEC-HMS model simulation reveals that the Wet condition (ARC-III) CN grid data predicted higher flood discharge than Dry and Average conditions. The peak flood discharge of 1,66,844 m3 /s, 1,97,926 m3 /s and 2,26,485 m3 /s predicted from model simulation based on Dry, Average and Wet conditions grid data respectively. The model simulation results shows that the Wet condition peak flood deliver a 26.33% higher discharge than Dry condition and 12.6% higher flood occurred than Average condition. The GCN250m grid data of ARC-III (Wet condition) condition weighted average Curve Number obtained a higher value, accordingly HEC-HMS model simulation results a higher flood discharge.