The Gumbel-hougaard Copula function was used to analyze the joint distributions between annual maximum daily storm and seven-day storm amounts which are both with Pearson type III marginal distributions.The rainfall data of the Geheyan reservoir during 1960 to 2002 were selected as a case study.The results show that a good agreement can be observed between theoretical joint and empirical distribution of annual maximum daily storm and the seven-day storm amounts.On the basis of the marginal and theoretical distributions of these two variables

the joint probability distribution and the related return periods of two variables can be deduced easily

much more exact design storm and storm processes can be obtained at certain condition.