This study proposes a new dynamic model of a time-varying switch bond graph for further improvement of the bond graph modelling method. The previous reference to the time-varying switch only discussed the on and off modes, but the dynamic model of a time-varying switch was not presented. This study proposes a bond graph modelling method of a timevarying switch which is mainly used for obtaining insights into the important dominant behaviour of the switch converter, such as the converter modelling, design of the controller, stability analysis and simulation of the converter; this is the reason why this study does not consider the multi-frequency modelling or generalised state-space averaging as the switch converter of a highfrequency switch behaviour.