De-emulsification of heavy oil emulsion is a great challenge to the oilfield production water treatment，which would cost very much due to the strong stability of the emulsion. Analysis of the emulsification mechanism is the fundamental to the further de-emulsification process. For the purpose of the potential treatment of the large amount of produced water-in-oil emulsions in Liaohe oilfield，the heavy oil properties were measured and re-emulsifying tests were conducted to investigate the emulsification mechanism of the heavy oil. The reasons on the heavy oil emulsion formation were also analyzed by considering the field in-situ production practice. Results show that the heavy oil emulsion in Liaohe oilfield has high water ratio up to 52%. The water is dispersed as small droplets in the heavy oil. The heavy oil also possesses high content of natural emulsifying agents based on which the heavy oil emulsion could be formed. The solid particles in the oil are mainly composed by quartz，and also high content of clay particles，most of which is montmorillonite with good dispersion and adsorption properties. The resins and asphaltenes take up to more than 24% in the hydrocarbons. The heavy oil possesses a high acidity of 5.47 mgKOH/g. The emulsifying mechanism of the heavy oil is determined by the external input energy，such as temperature，shearing and ultrasonic energy，and the stable oil-water interface film forms by the adsorption of solid particles and surfactants. The in-situ formed heavy oil emulsion is controlled by three factors of recover and transportation process，including the thermal recovery method and complex pipeline transportation system for the heavy oil，formation properties，including the high porosity，high permeability and high content of clay mineral composition，and heavy oil properties including the high acidity，high content of resins and asphaltenes，which provide favorable energy and substance for the heavy oil emulsification and finally resulting in the formation of large amount of water-in-heavy oil emulsions. The research findings provide experimental and theoretical foundations for subsequent emulsion demulsification in oilfields，offering indicative significance for crude oil dehydration treatment technologies.