Abstract: The capillary jet break up into a train of drops with artificial perturbation, which can be applied into many fields.Due to the small dimension and high velocity of the jet, especially for the jet in other liquid, it's very difficult to trackle the detail of the jet breakup.In this study, with the help of the dynamic mesh method and Volume of Fluids (VOF) method, the whole process including the application of the perturbation to the jet, jet breaking up into droplets, and droplets falling in the oil was simulated by the computational fluid dynamics (CFD) software FLUENT.The effect of perturbation frequency on the Sn-Bi jet breakup in silicon oil was studied.The results show that the fluctuation of jet velocity is found to account for the presence of necking of jet.With the increasing of the perturbation frequency, the diameter of the droplet decreases.The jet breakup length is the shortest when the optical perturbation frequency is applied, and the numerical results agree well with the experimental ones.