Topographical map of flood areas in the lower reaches of Jinpen Reservoir was generated by using GIS software to process basic data of Zhouzhi County and using interpolation method. The model for the rate of loss was used to assess the loss status of the inundated area. When the reservoir metthe flood of a return period of 10 000 years,the overtopping dam-break incidentcould occur and the flood could cause the directe-conomic loss to -5. 035 5 109RMB and indirecteconomic loss to -9. 0639 108RMB. Calculation and analysis of the loss by dam-break flood in this paper will enable policy makers and reservoir supervisors to know the consequences of the floods and help them to dispatch water volume rationally to avoid the disaster.