The water stages of tidal reaches are affected by upstream flood and downstream tide, thus, the analysis of the encountersof tide and flood in harnessing and planning for tidal reaches is indispensable. This paper took the tidal reaches of Oujiang asstudy area, and Gumbel Copula function was choosen to construct the joint probability distribution of flood and tide based on thestructure of the observed data, which is sensitive to the upper tail area. Then, the return periods were calculated and the riskmodels were established. And the rationality of different design standards was evaluated from the indexes of waterlogging preventionrisk, simultaneous risk and joint risk. The results show that Gumbel Copula function works well in showing the characteristics ofOujiang’s tidal reaches. The simultaneous return period, which combined twenty-year return period of the design standard and thetypical harmful tidal level (5.8m), is twenty-nine-year. And the rates of simultaneous risk, joint risk and waterlogging control riskare 3.46%, 11.52% and 15.94% respectively. Risk models based on Copula function can provide decision support and risk assessmentfor the design standard of waterlogging prevention in tidal reaches.