When a vacuum switch is introduced into gas insulation metal-enclosed switchgears（GIS） the mechanical reliability of the GIS will be endangered as the bellows of a vacuum interrupter will be subject to a high difference of gas pressure and high opening and closing velocities.However there remains little understanding on an influence of opening and closing velocities on the fatigue life of the bellows of the vacuum interrupter.The objective of this paper is to investigate the influence of opening velocity on the fatigue life of the bellows of the vacuum circuit breaker under high gas pressure circumstance.A 40.5 kV commercial vacuum interrupter is used as an investigating object.A fluid-structure coupling method is adopted to determine the transient relative displacement distribution of transient von-Mises stress as well as the fatigue life of the bellow structure under cases of 0.1～0.4 MPa difference of gas pressure and 1.0～4.0 m/s opening velocities respectively.Results show that:the maximum von-Mises stress increases with the increasing of the difference of gas pressure under a certain opening velocity;the maximum von-Mises stress increases with the increasing of the opening velocity linearly under a certain difference of gas pressure.The local stress of the bellows is concentrated and stepped up resulting from the spreading and reflecting of the stress wave during the depressing of the bellows.The maximum local stress can increase up to 1 500 MPa.The fatigue life of the bellow suddenly decreases when a high opening velocity is encountered under a high difference of gas pressure case.The fatigue life of the bellow is only 804 when the opening velocity is 4.0 m/s and the difference of the gap pressure is 0.4 MPa.