In this study, to analyze the flood stability of aged small reservoirs, the frequency rainfall and reservoir analysis was performed. At present, Simchun and Pyeungjuk freeboard are analyzed to be insufficient in the current reservoir condition and it is necessary to compensate for flood. As a result of analysis of freeboard, Simchun and Pyeungjuk were 1.22 m and 0.92 m, respectively, at the frequency of 200 years. In the hydraulic analysis, freeboard was analyzed as Simchun 1.24 m and Pyeungjuk 0.84 m. In comparison with hydrological and hydraulic analysis results at 200 year frequency, large storage Simchun was 0.02 m higher in hydraulic analysis and 0.06 m lower in pyeungjuk. Hydrological and hydraulic flood safety of the old reservoir was evaluated and the freeboard of the dam was examined. In addition to increasing the dam height in securing the safety of dam floods, it is necessary to study effective meathods.