This paper is concerned with modal analysis of an active framed structure by means of complex mode method. Theoretical and numerical results show that left mode shapes and right mode shapes of the active framed structure take on orthogonality with regard to structural parameter matrices. Also, left mode and right mode shapes have different physical meanings: right mode shape is the actual mode shape related to displacement, but the left mode shape is only a participant mode of external excitation, in other words, which characterizes the disturbed factor of external excitation for the active framed structure. The mode of the active structure is a primary indicator of the structural properties, and also is a target function of structural design, so mode study of the active structure is valuable in theory and practice. Finally, a numerical example is adopted to verify the above conclusions.