Abstract: A numerical method for identifying the aerodynamic admittance of bridge decks was proposed. A two-dimensional incompressible unsteady Reynolds average Navier-Stokes (URANS) approach with SST k-ω turbulence model was used. By generating an incoming flow with a smooth longitudinal component and a vertical single-frequency sinusoidal component velocity, the history of forces acting on the bridge deck was calculated through flow solution. Thus the aerodynamic admittance could be obtained by analyzing its spectrum. First of all, the self-sustaining capability of the generated inflow was studied and confirmed. Then a thin plate and a bridge deck section were taken to verify the method by comparing to the theory resolution and the experiment value. Finally, the initial condition for flow solution was discussed. The results showed that both the grid size and the time step should be small enough to keep the decay of the vertical sinusoidal component in an insignificant extent. The identified aerodynamic admittance of the thin plate got a quit perfect agreement with Sears function. The identified lift aerodynamic admittance of bridge deck was in accordance with Sears function in low reduced frequency, and less in high frequency, while it was closer to the experimental value. The identified moment aerodynamic admittance of bridge deck was also close to the experimental though it seemed different from Sears function. The initial condition of flow field had an effect on efficiency.