The rheological property of mayonnaise under different pressures is measured using AR 500 rheometer at low shear rate. The results show that Mayonnaise processed by high pressure is shear thinning fluid and takes on pseudoplastic characteristics. Taking the minimum standard error as the standard for best fit, the mathematic model of mayonnaise under different high pressure processing is obtained by using the constitutive equation of non Newtonian flow and measured data to fit curves, and the reason of viscosity variety in terms of pressure is analyzed tentatively. This is due to the protein molecule disassociated and unfolded with treatment of less than or equal to 500 MPa, while small molecule disassociated with the continuous increase of pressure may be associated over again, and increase of salad oil particle size in mayonnaise results in decrease of energy dissipation using slippage and friction beyond 500 MPa.