Abstract: Regarding microstate and rheological property, the paper studies the phase behaviors of the emulsions formed by the crude oil obtained from 81# combination station of Karamay oilfield and the aqueous dispersion system of Janus SiO2/PS nano-particles under the conditions of different mass fraction (CS) and different water-oil volume ratio (RWO). Setting CS=0.100%, when RWO≤7/3, stable water-in-oil emulsion is formed by the aqueous dispersion system of Janus SiO2/PS nano-particles and the crude oil, and both the droplet size and viscosity of the emulsion increase with the rise of the water-oil volume ratio; when RWO>7/3, the oil-water miscible liquid has 2 phases—the upper is water-in-oil emulsion and the lower is dominated by water, the viscosity of the emulsion decreases with the increase of the water-oil volume ratio. Setting RWO=7/3, when 0.080%≤CS≤0.300%, oil and water are mixed completely with the emulsion viscosity of more than 60 times of the crude oil viscosity, and the mixture becomes shear thinning at high shearing rate; when CS<0.080% or CS>0.300%, the oil-water miscible liquid has 2 phases and the emulsion viscosity decreases with the increase of the volume of separated water. Setting RWO=4/6, when 0.001%≤CS≤0.500%, oil and water are mixed completely with the emulsion viscosity of 55~75 mPa·s, and the emulsion becomes shear thickening at the shearing rate of 3.00~70.00 s-1. The results show that the aqueous dispersion system of Janus SiO2/PS nano-particles allows the crude oil to form stable, high-viscosity water-in-oil emulsion at relatively high water cut, and within a certain range of water-oil volume ratio, the higher the water cut, the higher the viscosity of the emulsion. The conclusion can provide a new idea for improving sweep efficiency in heterogeneous reservoirs