In order to analyze the adaptability of rational formula to the calculation of small watershed design flood in Turkey, this paper first introduced the widely-used Turkish flood calculation method—DSI Synthetic Method and analyzed its functions and characteristics in designing rainfall, runoff process and concentration principle. Then a comparison was made between the DSI Synthetic Method and two of the rational formulas which are commonly used in China. Further, this paper explored a synthetic method which combines Turkish rainfall and runoff principle and rational formula concentration principle to calculate small watershed design flood. At last, it compared the calculation results of the synthetic method and those of the DSI synthetic method. The calculation results show that the combination of rational formula with Turkish hydrological features is feasible for Turkish small watershed flood calculation