The first step of formulating flood risk management strategies is to identify the flood at-hazard areas. This study aims to map flood-prone areas with different hazard levels in the Dadu River basin, using simple additive weighting (SAW) and analytic hierarchy process (AHP) methods and the geographic information systems (GIS) tool. The grid map of selected criteria, rainfall, topography, drainage, and the usage of land were processed and applied to estimate the flood hazard index (FHI) values in the basin in the GIS environment. The resultant map illustrates the spatial distribution of basin-scale flood at-hazard areas, can be used as powerful guidance of implementing preventing and alleviating flood risk for decision-makers and managers, and extended application in other basins or disaster fields.