The viscous heavy oil near the emulsification reverse phase point had a large viscosity，which was extremely unfavorable for the exploitation and transportation of heavy oil. By examining the effect of temperature and stirring speed on the reverse phase point of heavy oil emulsification，suitable preparation condition for heavy oil emulsion was obtained. The effects of water soluble viscosity reducer and oil soluble viscosity reducer on the reverse phase point of heavy oil emulsification were investigated. The mechanism of emulsification inversion of heavy oil emulsion was analyzed from the viewpoint of interfacial membrane and agent action on asphaltene. The results showed that the emulsification reverse phase point of heavy oil emulsion reached the maximum on the preparation condition of 50℃ and 800 r/min stirring speed. Both the water soluble viscosity reducer and oil soluble viscosity reducer advanced the emulsification reverse phase point of heavy oil，but there was difference in advancing degree. With the increasing concentration of viscosity reducer，water soluble viscosity reducer decreased the emulsification reverse phase point of heavy oil from 48% to 35.6% ，while oil soluble viscosity reducer made the emulsification reverse phase point of heavy oil decreased first and then increased. Water soluble viscosity reducer achieved early phase reversal by decreasing the interfacial dilatational modulus and interfacial tension，while oil soluble viscosity reducer achieved phase reversal by decreasing the interfacial dilational modulus. The analysis of microcosmic morphology of asphaltene before and after adding viscosity reducer showed that water soluble viscosity reducer had higher extent of damage to asphaltene aggregates than oil soluble viscosity reducer. The viscosity reducer mainly realized phase reversal by reducing the strength of interfacial film formed by asphaltene.