With the change of global climate and the influence of human action,the analysis of drought characteristics has become a research hotspot.Because of the asymmetry of 2D variable in practical application, based on the asymmetric copula function proposed by Liebscher, the paper built 2D asymmetric copula function.Taking the daily flood data collected in Yichang hydrological station for example,the paper analyzed the Joint probability distribution of drought duration and peak value by use of 2D asymmetric copula function. It is proved that the law of variation of the correlation coefficient when a two-dimensional asymmetric copula is constructed, which can be used as a reference criterion for the selection of copula function. Bootstrap method of Rosenblatt transform is used to test the fitting degree of copula.Results show that the copula function can describe the probability distribution of drought characteristics.