Flood hazard zoning is one of the fundamental tools for natural hazard management and for reducing human and economic losses in watershed systems. The Rahim-Abad watershed in Fasa County, Fars Province, is considered a flood-prone area due to its specific hydro-geomorphological conditions and the frequent occurrence of flood events. This study adopts a descriptive–analytical approach to identify, weight, and prioritize the factors influencing flood susceptibility and to produce a flood hazard zoning map for the watershed. Hydrometric, synoptic, rainfall, and evaporation data from 16 stations with a 30-year statistical period (1989–2019), along with 1:5,000 topographic maps and 1:100,000 geological maps, were used in the analysis. Relevant flood-conditioning factors were identified using the Delphi method based on the opinions of 12 experts, and their relative importance was determined using the Analytic Hierarchy Process (AHP). The final criteria included curve number (CN), runoff depth, distance from waterways, slope and basin shape, drainage network, vegetation cover, soil type, and land use. The results indicate that hydrological factors play a dominant role in controlling flood susceptibility, with a final weight of 0.731. Among these, the curve number (CN) was identified as the most influential factor (weight = 0.559), followed by runoff depth (weight = 0.371). Spatial analysis revealed that the southern and downstream parts of the watershed are mainly classified as very high flood hazard zones, whereas the northern areas predominantly fall within the very low hazard class. Overall, the findings demonstrate that flood susceptibility in the Rahim-Abad watershed is not solely governed by topographic characteristics but results from the complex interaction of hydrological factors, land use patterns, and soil physical properties. The results can provide valuable support for watershed management, flood risk reduction, and land-use planning.