Abundant damage information is implicated in the bilinear time-frequency distribution of structural dynamic signals, which could provide effective support for structural damage identification. Signal time-frequency analysis methods are reviewed, and the characteristics of linear time-frequency distribution and bilinear time-frequency distribution, typically represented by the Wigner-Ville distribution, are compared. The existence of the cross-term and its application in structural damage detection are demonstrated. A method of extracting the dominant term is proposed that combines the short-time flourier spectrum and Wigner-Ville distribution. Then a two-dimensional time-frequency transformation matrix is constructed, and the complete cross-term is extracted. The distribution character is in favor of the structural damage identification. Through theoretical analysis, model experiments and numerical simulation of the girder structure, the change rate of the cross-term amplitude is validated to identify the damage location and degree. The effectiveness of the cross-term of the bilinear time-frequency distribution for damage detection is confirmed, and the analytical method of damage identification used in structural engineering is available.