The leading practice in mining fields has shown that the development effect of injecting supercritical multi-thermal fluids into heavy oil reservoirs is significantly better than steam flooding. However, the underground seepage law of injecting supercritical multi-thermal fluids is not yet clear. Therefore, the influence of reservoir wettability change on oil-phase relative permeability under the action of supercritical multi-thermal fluid is clear through supercritical multi-thermal fluid displacement experiment and contact Angle measurement experiment. Secondly, the oil-water and oil-gas phase permeability curves and the produced crude oil viscosity were obtained through the "high temperature and pressure steady-state method" experiment. Finally, based on the experimental data and Stone-II prediction model, different regions" isoperms of oil phase relative permeability are established. The study found that the contact Angle between oil sand and water decreases from 139.9° to 90.4° after injection of 5PV supercritical multi-thermal fluids, and the reservoir wettability becomes more hydrophilic, and the viscosity of produced heavy oil under supercritical water is reduced by 31.03% compared with steam. The characteristic values of the oil-water relative permeability curve change gradually with increasing temperature, but when the temperature and pressure reach the supercritical state, the characteristic values of the curve undergo a sudden change, and the residual oil saturation decreases significantly from 24.8% to 6.9%. The characteristic values of the oil-gas relative permeability curve gradually change with increasing temperature. In the isoperms of oil phase relative permeability, the oil phase equal permeability line is a curve concave toward the 100% oil saturation point, with denser equal permeability lines as the oil saturation increases. As the temperature increases, the curvature radius of the oil phase equal permeability line gradually increases, and the area of the oil phase flow region gradually increases. When the temperature rises to 400°C and the pressure increases to 22.5 MPa, the size of the oil phase flow region significantly increases from 38.86% to 52.66%. When the temperature continues to increase to 420℃, the size of the oil phase flow zone increases to 54.59%, and the flow capacity of the oil phase significantly enhances. The research results of this paper can provide a theoretical basis for the numerical simulation of injecting supercritical multi-thermal fluids into heavy oil reservoirs.