To address the problem that the calculation method of the design value combination of flood peak and flood volume under stationary conditions cannot be applied for the non-stationary case under changing environment, this paper firstly constructs the multi-dimensional joint distribution model with time-varying dynamic Copula function, which can comprehensively consider the non-stationarities of marginal distributions and correlation structure between variables of the flood peak and flood volume. Then the nonstationary evolution characteristics of the joint distribution of flood peak and flood volume over time are analyzed. Subsequently, based on the equivalent reliability method and the conditional expectation combination method, the calculation method of design value combination of the flood peak and flood volume under changing environment is proposed, which can be applied to estimate the expected design value of flood peak and flood volume combination with a given return period under the changing environment. Taking the flood peak and maximum 7-day flood volume series at the Huanglongtan Station as examples, a case study is conducted. The results show that the joint distribution characteristics of flood peak and flood volume changes significantly with time, and the expected combination design value of flood peak and flood volume corresponding to the specified return period is affected by engineering design lifetime with a decreasing trend as the design lifetime increases.