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When identifying the aerodynamic derivatives of parallel separated double-deck bridges using free-vibration testing method (FreeV method), the different initial manual excitations produce different aerodynamic interference between two sectional models, which cause the identification results are always significant discrete and irregular. Therefore, the mixed forced-vibration testing method (MFV method) is proposed in this article. The aerodynamic derivatives identified by FreeV method and MFV method are compared and analysed. The flutter analysis results based on the FreeV and MFV method are also in contrast with the test results. Research results show that, no matter the windward deck or the leeward deck, the aerodynamic derivatives identified by MFV method put up to small dispersions and good laws of variation with reduced wind speed. However, the aerodynamic derivatives obtained by FreeV method show larger dispersions and worse variation laws, especially those of the leeward deck which suffered from aerodynamic interference seriously. Furthermore, the flutter critical wind speeds calculated based on the MFV method are rather close to the test results, whereas those based on the FreeV method have a big discrepancies with the test results, especially those of leeward bridge. In contrast with the FreeV method, the MFV method could simulate the aerodynamic interference effect rationally and the flutter prediction results are more accurate. [ABSTRACT FROM AUTHOR]