Aiming at assisting the steam injection technology for thermal recovery of offshore heavy oil in Bohai oilfield，the self-made water-soluble high temperature emulsified viscosity reducer SP was introduced to form an aqueous surfactant solution where the O/W emulsion was prepared with the oil-water mass ratio of 70∶30. The effects of salinity，pH value，temperature， surfactant concentration on the stability of emulsion were studied. Moreover，the effluent rate of 60 min resting at 50℃ was picked to determine the stability of the system. The higher the water yield，the worse the stability was. In addition，the stability mechanism of emulsion was analyzed by measuring the interfacial tension between surfactant solution and heavy oil. The results showed that the influence of salinity and pH value on the stability of emulsion was the greatest，followed by the dosage of SP，and the effect of temperature was smaller. With the increase of salinity，the interfacial tension and effluent rate decreased first and then increased. It was found to produce the minimum interfacial tension and the best stability under the condition of 55 g/L salinity. Compared with sodium ion，calcium ion played a dominate role on the interfacial tension，and the alkalinity condition promoted the system stability.With the decrease of surfactant concentration，the interfacial tension of the system increased while the stability of emulsion decreased. The optimum emulsifying temperature range of SP was found to be 50—70℃，and the activity of self-made SP was acceptable after 300℃ treatment，indicating that SP was not sensitive to high temperature. Thus，SP was suitable for the steam injection technology for thermal recovery of heavy oil.