Abstract: The viscosity of heavy oil is high, so its exploitation and transportation is more difficult.To solve this problem, its viscosity has to be reduced by means of emulsification.Therefore, it is quite important to study the characteristics of its emulsion.In this paper, the effects of surfactant type & content, oil/water ratio, emulsifying temperature and emulsifying intensity on the stability and rheological property of heavy O/W emulsion were studied by means of single-factor experiments.It is shown that the stable emulsions prepared by different types of surfactants have large differences in stability and rheological property.With the mass fraction increase of CAB-35, the water separation rate of emulsion decreases firstly and then changes insignificantly, while its apparent viscosity increases firstly and then changes insignificantly.With the increase of oil/water ratio, the water separation rate of emulsion decreases and its apparent viscosity increases gradually.With the increase of emulsifying temperature, the water separation rate of emulsion decreases firstly and then increases and its apparent viscosity decreases gradually.With the increase of emulsifying intensity, the water separation rate of emulsion decreases gradually and its apparent viscosity increases firstly and then stays at a stable value.The optimal emulsification condition was determined by considering stability and rheological property comprehensively.The research results provide the theoretical basis for the emulsification based viscosity reduction of heavy O/W emulsion.