The main objective of this study is to discuss the joint distribution of strong wind and rainstorm and its impacts on the design value of dam crest elevation. Taking Donghu Reservoir as the study object, we conducted marginal distribution fitting between maximum wind speed and three sets of rainfall series using GEV, Gamma, and P-Ⅲ distribution respectively. Based on the joint probability distribution of maximum wind speed and rainfall series constructed by the binary Copula functions, the design values of wind speed and rainstorm of 100-year return period were estimated and the crest elevation of the main dam was re-checked whether it met the safety requirements. The results show that the annual maximum daily rainfall presented a significant upward trend (P<0.05), whereas the annual maximum wind speed featured a non-significant one, and the maximum rainfall event once occurred at the same time with the maximum wind event. As for the encounter analysis, both the calculated values of maximum wind speed and rainfall showed a rule as “joint return period > univariate return period > co-occurrence return period”, of which the value of maximum wind speed of joint return period was only approximately 10% larger than that of univariate return period. The estimated value of crest elevation based on joint return period was lower than the actual value of the wave wall, indicating that the crest elevation of the main dam could meet the safety requirements of the encounter of strong wind and rainstorm (100-yr). The results of this study can provide references for the calculation of design wind speed and crest elevation of reservoir dams in the coastal regions of China.