The relevant theories and principles of structural dynamic characteristics are more and more widely used in various engineering fields, but the understanding and mastery of their basic concepts and principles still need to be further promoted. Some basic concepts seem to be very basic and perfect, but without accurate understanding and mastery, it is difficult to apply them to engineering practice scientifically. Based on theoretical analysis, some common problems in structural dynamics, such as structural natural frequency and circular frequency, structural first natural frequency and fundamental frequency, structural damping and modal damping ratio of multi-degree-of-freedom system, application of natural frequency in bridge technical state evaluation, Rayleigh quotient annotation and so on, are deeply analyzed and analyzed, and some basic concepts are clarified. It makes the theoretical system of structural dynamics more complete.