To discern false modes during experimental modal analysis process and identify dense modes in axial symmetrical structures, the dynamic properties of truncated conic aluminum alloy thin shell satellite adaptor was experimental investigated. Electromagnetic vibration generators were used for exciting structures, and piezoelectric accelerometers for measuring the corresponding response. Polynomial method was applied for fitting experimental frequency response functions and identifying modal parameters. The effects of different methods between single input single output (SISO), single input multiple output (SIMO), and multiple input multiple output (MIMO) were evaluated systematically, both experimental and numerical analysis results were compared to recognize false modes. The experimental results show that the MIMO method helps in splitting dense modes in axial symmetry structures, and the former 10 modes of satellite adaptor were clearly identified. However, improper exciter fixation results in false modes in frequency response function. For experimental modal analysis of lightweight structures, special attention should be paid on additional mass and stiffness due to exciter fixation.