Due to the risk of the billet hitting the marking equipment, it is necessary to design a set of anti-collision mechanism. When the billet hits the marking equipment, the marking gun goes back and the positioning pins are pulled out by a scotch-yoke mechanism. Then the support arms lift to avoid the billet. Before the impact, the anti-collision mechanism performs as a gun frame, carrying the gun moving. However, the vibration may have an adverse impact on the marking effect. The maximum force appears when the marking gun is moving in the accelerative stage in X and Y orientations. The load and boundary conditions were set according to the actual load condition of the anti-collision mechanism. The harmonic response analysis calculated the amplitude of X and Y orientations of the marking gun at different frequencies. Then the structure of the anti-collision mechanism was improved and the harmonic response analysis was done again. The results show that the amplitude of the improved structure has been reduced dramatically and the marking effect has been improved.