In recent years, the frequency and severity of flood events have increased globally, causing severe disasters. Therefore, we may need flood risk assessment to support decision-making for flood damage reduction and this study conducted flood risk assessment by Indicator based Approach (IBA) using two items of Hazard and Exposure which have five indicators of maximum rainfall, peak discharge, water level, industrial area, and residential area for the Gapcheon Stream Basin in South Korea. The frequency analysis was performed for hourly rainfall data by FARD 2006 and obtained the 24-hour rainfall data corresponding to different return periods (including 5-year, 10-year, 20-year, 50-year, 100-year and 200-year return periods) which are input into the hydrological model, HEC-HMS. Then we obtained peak discharge values and hydrographs. Integrating the obtained peak discharge data into the hydraulic model HEC-RAS helps to generate a comprehensive water surface profile or water level of the river. The primary objective is to perform flood risk assessment by applying Euclidean distance for five indicators to calculate the flood risk index based on the simulated peak discharge and water level. Flood events were the focus of both the 2011 and 2020 study periods and we obtained Hazard Index 1 (simulation) and Hazard Index 2 (observation) in assessing flood risks across 6 subbasins. Hazard Index 1 generally decreased in 2020, while Hazard Index 2 showed fluctuations. The Flood Risk Index, derived from these Hazard Indices, exhibits significant variations between simulation and observation, emphasizing the impact of simulation versus observation on flood risk assessment. Gabcheonhalyu subbasin shows a substantial increase in both Flood Risk Indices, while Yudeungcheonhalyu subbasin demonstrates a decrease in Flood Risk Index 1 but an increase in Flood Risk Index 2, highlighting the importance of considering both industrial and residential areas in flood risk assessments. Therefore, we may need more studies for the simulated and the observed Flood Risk Indices to examine their variations and correlations.