In order to deeply understand the mechanism responsible for the emulsifying viscosity reduction for heavy oil in chemical flooding，the interfacial tension and dilational rheological parameters between heavy oil and three polyether solutions with different structures were studied. The stability，particle size and viscosity of the emulsion that was formed by polyether solution and heavy oil were also investigated. The results showed that long flexible ethylene oxide（EO）and propylene oxide（PO）chains in polyether molecule could form a sub-layer at interface，resulting in an oil-water interfacial film with strongly elastic nature. Therefore，it was easy for polyether solution to form stable O/W emulsion with heavy oil and obviously decrease viscosity. The molecular weight and the ratio of EO/PO played the major role in affecting interfacial tension and the strength of interfacial film was mainly controlled by molecular weight. The polyether with larger molecular weight showed higher interfacial film strength and more stable O/W emulsion with heavy oil. The structure and dosage of polyether and oil-water volume ratio showed little influences on particle size of emulsion，which varied from 300 nm to 500 nm. The three polyether solutions with molecular weight of 8400，12600 and 14600 had good viscosity reduction effect on heavy oil. At oil-water volume ratio of 1∶1，the rate of viscosity reduction was over 98% when the dosage of polyether was 0.2% —0.5% . The molecular weight and the ratio of EO/PO had little effect on viscosity reduction.