To solve the problem of unclear comparison and optimization methods for viscosity reducers in the development of chemical viscosity reduction for heavy oil， a quantitative relationship between the properties of viscosity reducers and their oil displacement efficiency was established using laboratory experiments and mathematical analysis methods. The quantitative relationship between the various properties and the oil displacement efficiency of the viscosity reducers was determined by using the linear regression method for a single-factor analysis. Based on the correlation coefficient in the regression， the main properties affecting oil displacement efficiency were clarified. Two indicators， namely oil displacement degree and oil displacement index， were proposed，and a calculation method for the oil displacement index that reflected the oil displacement efficiency was established. Research shows that the minimum emulsification speed， viscosity reduction rate， particle size of emulsion， and adsorption loss are the main properties affecting oil displacement efficiency. Dehydration rate and oil washing efficiency have a certain impact on oil displacement efficiency. In the low interfacial tension range， the influence of interfacial tension is not significant. The minimum emulsification speed， particle size of emulsion， adsorption loss， and dehydration rate are negatively correlated with oil displacement efficiency，while viscosity reduction rate and oil washing efficiency are positively correlated with oil displacement efficiency. A viscosity reducer featuring easy emulsification， high oil droplet passability after emulsification， strong anti-adsorption ability， strong flowability of emulsified crude oil， and strong stripping effect on crude oil is more likely to achieve higher oil displacement efficiency.The oil displacement index and oil displacement efficiency are linearly positively correlated， and the index can reflect the oil displacement efficiency. The rationality and practicality of the evaluation method have been verified through viscosity reduction stimulation and viscosity reduction displacement tests in the mining field.