Structural modeling and dynamical analysis of rotating composite shaft are conducted in this paper. A thin-walled composite shaft structure model, which includes the transverse shear deformation of the shaft, rigid disks and the flexible bearings, is presented and then used to predict natural frequencies and dynamical stability. Based on the thin-walled composite beam theory referred to as variational asymptotically method (VAM), the displacement and strain fields of the shaft are described. Hamiltonโs principle is employed to derive the equations of motion of the shaft system. Galerkinโs method is used to discretize and solve the governing equations. The validity of the model is proved by comparing the results with those in literatures and convergence examination. The effects of fiber orientation, ratios of length over radius, ratios of radius over thickness and shear deformation on natural frequency and critical speeds are investigated. Finally the unbalance transient responses of the composite shaft system are also given by using the time-integration method