Abstract: A temporal instability analysis of an electrified coaxial liquid-gas jet was performed based on the simplified theoretical model of the flow focusing under an electric field.On the assumption that the fluids are inviscid,an analytical dispersion relation of disturbances growing in the temporal regime was obtained and the effects of main controllable parameters on the unstable modes were analyzed.The results indicate that,only the axisymmetric and the first non-axisymmetric disturbances grow in the temporal regime;the surface tension has two-fold influences on the axisymmetric instabilities and suppresses the non-axisymmetric instabilities;the increases of velocity and density of the external gas streams can definitely promote the jet instabilities.These conclusions are consistent with the experimental results qualitatively.The results also show that the single axial electric field can suppress the jet instability when the initial electric charge density on the jet surface is neglected.On the whole,the theoretical investigation will be helpful for understanding the physical mechanisms of the flow focusing under an electric field and for providing guidance to practical applications.