The invention relates to the field of lubricating oil, and discloses a method of using polymer to modify a lubricating oil. The method comprises a step of directly mixing a polymer solution obtained after polymerization reactions with a lubricating oil basic oil, wherein the polymer is at least one of ethylene propylene rubber, hydrogenated styrene-butadiene block polymer, and hydrogenated styrene-isoprene block polymer. According to a conventional method, a solid lubricating oil viscosity index modifier is used to modify a lubricating oil basic oil, the flowing performance of the modified lubricating oil at a super low temperature is not improved, the viscosity of the modified lubricating oil is not high enough at a high temperature, and the viscosity-temperature defect of the lubricatingoil is not overcome. The provided method overcomes the abovementioned problems. The obtained modified lubricating oil product has excellent viscosity-temperature characteristics.