Studying on reducing viscosity by emulsifying of Xintan heavy oil of Shenli oilfield, it is found that W/O/W poly-phase emulsion dripping will be formed partly while preparing the heavy oil O/W emulsion. The quantity and property of such poly-phase emulsion dripping is related to methods of preparing O/W emulsification. As the O/W emulsion is prepared with the pure heavy oil and active water directly, the poly-phase emulsion dripping formed is a little. The reason is that the oil-water interface film between middle oil phase and external water phase is damaged. It has little effects on the stability of the whole emulsion. However, much more W/O/W poly-phase emulsion drippings are formed when preparing O/W emulsion by utilizing the method of phase inversion with high containing water W/O emulsion. It has great effects on the stability of the whole emulsion.