Abstract: The vacuum arc extinguishing chamber, as the core component of the vacuum on-load tap-changer (OLTC), determines the reliability of load switching through its successful closing. During the long-term operation of the vacuum OLTC, the vacuum arc extinguishing chamber frequently suffers significant mechanical impacts, which may lead to fatigue damage, causing closing failure of contact and affecting the reliability of the switching operation. This paper takes the vacuum arc extinguishing chamber and its operating mechanism of the oil-immersed vacuum OLTC as the research subjects, establishes a dynamic model and a finite element model describing the contact collision process, obtains the stress wave propagation patterns during the closing process, identifies the parts prone to fatigue damage, and studies the main factors affecting stress and contact bounce. The results show that, when the collision velocity of the moving contact is within 1 m/s, it is not until the initial closing collision that the closing pressure becomes the main factor affecting the bounce of the contact; significant closing bounce occurs during closing, and the stress on the connecting rod rapidly increases, fluctuating between multiple peaks, making it more susceptible to mechanical damage under cyclic stress; increasing the radius of the static conductor rod has a negligible effect on rebound but increases the maximum stress significantly; increasing the radius of the connecting rod or the moving conductor increases the rebound and decreases the maximum stress; increasing the closing holding force decreases the rebound without changing the maximum stress obviously; reducing the closing speed helps to reduce both the maximum stress and the rebound. The research results of this paper can provide theoretical guidance for optimizing designs of the vacuum arc extinguishing chamber in vacuum OLTCs.