Fluidic oscillator is a device which can generate unsteady flow at the outlet, when supplied with steady flow at the inlet. In this paper, numerical simulation is used to research the internal flow field characteristics of a fluidic oscillator, as well as the reverse flow characteristics and switching mechanism. The main jet flows along one of the outlet, and the reverse flow is generated in another outlet due to the effect of the low pressure area of the cavity. The reflux degree decreases with the increasing of the pressure ratio and ambient temperature, and increases with the increasing of the splitting distance. The flow rate ratio between inlet and outlet decreases with the increasing of control flow , and then the jet is switched when continue to increase the control flow. And the results presented in the paper can be applied to some significance for the study of fluidic oscillators design.