This paper studies the damping vibration properties of the big damping bar by the generalized multisymplectic method based on the Bridges’s multisymplectic method and the Hamilton variation principle. Introducing orthogonal momenta, a firstorder approximate symplectic form, named generalized multisymplectic form is derived from the control equation of the big damping bar vibration firstly. And then a midpoint Box generalized multisymplectic scheme is constructed by the midpoint method; Finally, the dissipation effect of the big damping bar vibration is studied. From the results of the numerical experiment, the good properties of the generalized multisymplectic method are verified: satisfying the conservative properties of the system and reproducing the dissipation effect of the system.