The invention relates to a method for extracting dicyclopentadiene from a petroleum cracking to ethylene byproduct C9-C10 fractions obtained by petroleum cracking. The method comprises the following steps: depolymerizing and rectifying the C9-C10 fractions to obtain a cyclopentadiene fraction at the top of the tower and methyl cyclopentadiene on a lateral line as well as residual fractions in a tower kettle; then, carrying out reduced pressure distillation on the residual fractions in the tower kettle to obtain a styrene-enriching fraction at the top of the tower; then, carrying out reduced pressure distillation on the fractions in the tower kettle of a reduced pressure distillation tower to obtain a dicyclopentadiene-enriching fraction at the top of the tower, returning the dicyclopentadiene-enriching fraction to raw materials, mixing the dicyclopentadiene-enriching fraction with the raw materials, feeding the mixture into a depolymerizing and rectifying tower and separating; and carrying out reduced pressure distillation on the materials in the tower kettle by a reduced pressure distillation tower to obtain indene and methyl cyclopentadiene fractions at the top of the tower and heavy components in the tower kettle. The method provided by the invention is used for obtaining high-purity cyclopentadiene, methyl cyclopentadiene and styrene products while obtaining excellent petroleum resin raw materials. In the rectifying and separating process, dimerization reactions are greatly reduced, and the yield of dicyclopentadiene is improved by the technical means of returning unreacted dicyclopentadiene material in the depolymerizing and rectifying tower to be mixed with the raw materials.