Abstract: Amechanical model for concrete stirring bars is proposed and its fourth-order partial differential equation is derived. The bars are idealized to free-free beams with lumped mass. The corresponding frequency equation is also derived from the solutions to the differential equation, the boundary conditions and continuous condition at the lumped mass. The dynamic characteristics of the stirring bars are obtained. The relationship among the position and eccentric distance of the vibrator, the dimension of the stirring bar and the vibrating frequency is discussed.