As for the problem that the rare flood frequency design value is too large with parameter estimation methods, this paper used the FIT method of order statistic expectation value to calculate the initial value of design flood. For the problem that the common flood frequency design value is too small with parameter estimation methods, this paper used the ZhouWende formula to calculate the correction value of design flood. As for the problem that the error of design flood is too large, this paper used the standard deviation of generalized order statistics method to calculate the safety value of design flood.The results show that the FIT method of order statistic expectation has a good unbiased and effectiveness properties. The correction value of design flood of the Cuntan station design flood is greater than the initial value of design flood, and both bias decreases as the frequency decreases. Obviously, the safety value of design flood of Cuntan Station design flood is greater than the correction value of design flood.