Abstract: Taking Tieshan Harbor Area as an example,based on the function superiority evaluation method,P-Ⅲ type and generalized Pareto distribution are selected as the edge distribution models of rainfall and corresponding tide level respectively. Based on the graphic evaluation method,GH copula function is selected to construct the joint distribution of rain and tide level,the return period is designed by considering the combination of rain and tide,and the concept of secondary return period is introduced. By comparing the differences between the traditional return period and the secondary return period under different combinations of rain and tide,it is obtained that the range of rain and tide dangerous events defined by the secondary return period is wider and safer than that defined by the traditional return period,and the occurrence risk rate and conditional risk rate under different combinations of rain and tide levels are analyzed so as to provide a scientific basis for the flood control planning of Tieshan Harbor.