The characteristics of joint probability distribution of flood were analyzed between the Makou Station(MS) in Xijiang River and the Sanshui Station(SS) in Beijiang River which are connected by the Sixianjiao Channal based on Copula function Some conclusions were abtained as following: (1) Optimized marginal distributions of flood of Makou and Sanshui can be represended by the Pearson pattern Ⅲand GEV (generalized extreme value) distribution

respectively; (2) GumbelHougaard Copula was the optimal copula selected by the results of goodnessoffit test; (3) The relative differences of the special frequency design values between the marginal distribution of Makou and Sanshui floods and the joint distribution were from 0.6% to 1.5% for the return periods between 10 years and 500 years; (4) The probabilities of Makou and Sanshui meeting floods with each other were higher than 89% for the same design frequencies of two stations based on the conditional probability.