Abstract: Assuming that the population model of flood stochastic process is known, the precison of design flood-control storage calculated by the traditional and the flood simulative method is preliminarily compared. The criterion of the precison evaluation is unbiasness and efficiency of design flood-control storge. In the traditional methods, two design flood hydrgraph enlarging methods are considered, one is same-frequency method, the other is same-multiple method. The Monte-Carlo results shows that the precision of design flood-control storage calculted by the flood simulation method is better than the traditional methods and the same-frequency method is better than the same-multiple method if the form of flood simulation model is correct.