Abstract: Vacuum-type on-load tap changer (OLTC) has the advantages of strong arc extinguishing ability, oil-free carbonization pollution, and has been widely used in on-load voltage regulation of converter transformers. Vacuum OLTC has complicated mechanical structures, and the switching action has strict sequence and time requirements. It needs to withstand huge mechanical and current impacts during frequent actions, which may trigger mechanical failures, affecting the safe operation of transformers and converter stations. In order to further explore the mechanical characteristics of vacuum OLTC during switching, this paper takes a three-phase vacuum OLTC as the research object, introduces the mechanical structure and operation characteristics of the diverter switch of the vacuum OLTC, proposes a multi-body dynamics simulation modeling method of the diverter switch of the vacuum OLTC, and calculates the dynamic characteristics of the key components of the diverter switch. The result shows that the action sequence of the diverter switch is reasonable and the process of contact switching is accurate, but the impact force of the fast mechanism on the components is relatively large. On this basis, this paper explores the influence of counterweight and buffer mechanism on the dynamic characteristics of the switch, and redesigns the buffer mechanism of the diverter switch. The result shows that the new buffer mechanism can effectively reduce the switching impact. The research method in this paper can provide a useful reference for improving the mechanical stability and reliability of the OLTC.