The invention relates to a separation method for ethylene byproducts, namely C9-C10 fractions produced by petroleum cracking. The separation method comprises the following steps: performing depolymerization and distillation on the C9-C10 fractions to obtain a cyclopentadiene fraction at the top of a tower, obtain methyl cyclopentadiene on a sideline and obtain remaining fractions in a tower kettle; then performing reduced pressure distillation on the fractions in the tower kettle to obtain styrene and methyl styrene fractions at the top of the tower and the fractions in the tower kettle; further performing reduced pressure distillation on the fractions in the tower kettle to separate a mixed fraction of indene and dicyclopentadiene and a heavy component; and finally performing depolymerization and distillation on the fractions at the top of the tower to separate two fractions, namely cyclopentadiene and indene. According to the separation method provided by the invention, a high-quality petroleum resin raw material is obtained, and high-purity cyclopentadiene and methyl cyclopentadiene are simultaneously obtained; dimerization in a distillation separation process is greatly reduced, the whole process can be considered to have no circulating materials basically, the generation of polymers is avoided, and the single-pass product yield is higher; simultaneously, the improvement of the process also solves the contradiction in difficult separation of dicyclopentadiene and indene.