Abstract: The impact of complex wavefields on the ultimate aseismic capacity of high gravity dams remains an area requiring a comprehensive investigation. This study addresses this gap by performing a nonlinear dynamic analysis of a typical high-gravity dam in southeastern China. In the investigation, the random wavefield method was introduced to generate the site-specific wavefield and motion field fit for the seismic response of gravity dams. The Concrete Damage Plasticity (CDP) model was employed to capture the nonlinear behavior of concrete. Two input schemes, the vertical incidence and the complex wavefield, were designed to calculate the dam's failure process under the action of wave fields corresponding to different Ground Acceleration Peaks (GAP). The results indicate that the spatial distribution of failure areas is similar under both schemes. And the failure patterns of the gravity dam under two input schemes are both from the upper part of the downstream face to the upstream face. The extent of failure is significantly greater for the complex wavefield scheme, since the cumulative plastic dissipation energy under this scheme is approximately double that of the vertical incidence one. The sliding stability safety factor remains high across all cases, even after the cut-through of failure areas. Considering the cumulative plastic dissipation energy, the development of failure areas, and the sliding stability safety factors, the ultimate seismic capacity of this gravity dam under the vertical incidence scheme is 0.84g, 0.95g, and 0.80g, respectively, for three wavefield conditions. In comparison, the corresponding values under the complex wavefield scheme are 0.75g, 0.80g, and 0.74g. The complex wavefield significantly reduces the ultimate aseismic capacity of the high-gravity dam, with a maximum reduction of 0.15g observed among the three wavefield conditions investigated.