Abstract: In the traditional teaching of vibration mechanics, the complex modes have been used to decouple the systems as a manipulation tool. The physical meaning of the complex modes is not clearly transferred. In this paper, the relationship between the combo of displacement and velocity of every oscillators have been demonstrated as the system shows the complex modes, illustrated by a 2DOF rotating system. The non-uniform and following features of the complex modes have been discussed, which give visual physical meaning to the beginners of the vibration course.