The invention belongs to the technical field of oil exploitation, and particularly relates to a chemical flooding method of a heavy oil reservoir. The chemical flooding method of the heavy oil reservoir includes the steps that a polymer water solution or polymer jelly is sequentially injected into a reservoir stratum to form a polymer front slug, a polymer body slug and a polymer rear slug, wherein the number-average molecular weight of a polymer is 28,000,000-36,000,000. According to the chemical flooding method, the swept volume of polymer flooding is increased, the oil flooding efficiency of polymer flooding is improved, and the purpose of increasing the crude oil recovery rate can be achieved on the premise of the low exploitation cost.