In order to study the effects of pulsing wind parameters and structural motion state on the complex aerodynamic admittance functions（AAF）of bluff body，a new procedure to generate the vertical- and along-wind harmonic inflows in CFD simulations is proposed. Based on the N-S equation and the boundary condition，this method can well control the amplitude and generate multi-frequency harmonic inflows. The lift and drag AAFs of a rectangular section with aspect ratio of 4 are identified under different wind attack angles and three different harmonic amplitudes. The aerodynamic admittances are compared under the multi-frequency harmonic combinations as well as the vertical and torsional motions. It is shown that the lift admittance at null attack angle is in good agreement with the experimental data. The wind angle attack and harmonic amplitude have a significant impact on the complex admittance. In addition，the lift AAFs remain almost the same in multi-frequency inflows and different motions，while the torsional motion can increase the value of drag AAF at high frequencies.