The bifurcation behaviors and chaotic vibrations of transmission viscoelastic belts were investigated. An improved model of axially moving viscoelastic beam with small stiffness was introduced; the nonlinear effects of deflection and material were considered simultaneously, the partial differential dynamical equations for the visco-elastic belt were established using elastic mechanics method. The method of Galerkin approach was applied to obtain the secondorder nonlinear equations,which decoupled in time and space coordinates. The effect of the velocity perturbation of the belts was discussed emphatically. Numerical simulation method was used to yield the response of the system; the bifurcation figure and Poincaré map show that the belts may undergo periodic and chaotic motions around different equilibrium in certain parameter regions, and the chaotic motion will occur through period double bifurcation.