The ring molding machine is the main equipment for dense forming of biomass, and its working stability is affected by severe vibration problem during the forming process, which reduces the forming quality of biomass. Therefore, aiming at the vibration problem of the ring molding machine during the forming process, the dynamic simulation model and the discrete element model of the ring molding machine were established by RecurDyn and EDEM respectively according to the actual working conditions, and the snapping process of the ring molding machine was simulated by co-simulation. Then, according to the co-simulation results, the extrusion force conditions of the ring die under different spindle rotation speeds were obtained, and the equivalent stress cloud diagram of ring die was obtained by the finite element software. The results show that the maximum equivalent stress on the ring die is 95. 930 MPa, which occurs at the entrance of die hole for the ring die. Taking the maximum extrusion force on the ring die as the load, the prestressed modal analysis and the harmonic response analysis of the ring molding machine were conducted. According to the prestressed modal analysis, the deformation of the ring molding machine was mainly manifested as swing and torsion, and based on the harmonic response analysis, the amplitude-frequency curves of the ring molding machine in the X, Y and Z directions were obtained. The results show that the resonance in the ring molding machine is easy to occur at the first order, third order and the fifth order natural frequencies, and the operation near these excitation frequencies should be avoided.