Abstract: The dynamic characteristics of a three-dimensional(3D) flexible rotating beam is studied. Using the absolute node coordinate formulation and geometric nonlinear deformation hypothesis, the nonlinear dynamic model of 3D flexible beam is established based on the general continuum theory. Based on the perturbation theory and the floating-point coordinate method, the vibration frequency domain analysis model of the rotating flexible beam is established by using the linearization technique. Then, the time domain simulation of the free single pendulum of the flexible beam is carried out, and the frequency domain characteristics of the 3D flexible rotating beam at different speeds are analyzed. The results show that as the rotation speed increases, its dynamic stiffening phenomenon is obvious, and the frequency corresponding to the mode shape of the vertical rotation plane and the torsional and tensile modes will gradually be transformed into low-order frequencies, thereby affecting the vibration characteristics of the flexible beam.