To address the critical issue of microstructural degradation and dynamic failure of Cu-Ni alloys subjected to multiple stress couplings in flowing seawater, this study systematically investigates the microstructural evolution and failure characteristics of the alloy in a complex service environment. Focusing on the widely used B10 Cu-Ni alloy in pipeline systems, a combined experimental and computational simulation approach was employed. A molecular dynamics method was used to construct an alloy/seawater solvation model, with emphasis on the effects of seawater flow rate, pressure, and their coupled interactions on microstructural evolution and corrosion kinetics. In flowing seawater, the strain level of the alloy increases markedly, accompanied by a rise in microstructural defects. The results reveal that corrosion of Cu-Ni alloys proceeds through a multi-step coupled mechanism governed by the migration-dissolution energy barrier of Cu atoms. Density functional theory calculations show that as seawater pressure increases from 0.1 MPa to 12 MPa, the migration-dissolution energy barrier decreases from 1.76 eV to 1.54 eV, significantly accelerating the corrosion rate. Furthermore, increasing seawater flow rate induces atomic-level axial elastic tensile strain on the (111) crystal plane of the alloy, further reducing the migration-dissolution energy barrier. A critical flow rate of 4 m/s has been identified as exacerbating corrosion. Under the coupled influence of flow rate and pressure, the migration-dissolution energy barrier is further reduced, the work function decreases, and corrosion kinetics are significantly accelerated. The corrosion rate constants obtained from simulations exhibit highly consistent trends with experimentally measured corrosion rates, enabling reliable assessment and prediction of the corrosion tendency of the B10 Cu-Ni alloy during dynamic failure under real operational conditions.