Abstract: The model used in high-frequency-force-balance test must be light and rigid. However, for lattice-truss structures, it is difficult to ensure rigidity of their wind tunnel models due to structural features and model fabrication limits. Force data of a semi-rigid model measured by a force balance needs to be modified before applying them in vibration analysis of the prototype structure. Based on D'Alembert's principle and mode superposition method, assuming the transformation relation between the prototype mode and the modal mode, a new formula for modifying modal force spectra of a semi-rigid model was obtained. With the aid of the newly derived formula, the traditional frequency domain analysis method can be used to predict wind-induced response of a lattice-truss tower structure. The wind tunnel test was conducted for a large-scale tower installed with a boiler. After applying the new formula, modal force spectra measured in the wind tunnel was corrected. Wind-induced response analysis was performed successfully for this tower structure. The results validated the adequacy of structural design of this tower in resisting wind storm.