Method of separating C5 fraction by using DMF mixed solvent

The invention discloses a method of separating C5 fraction by using a DMF mixed solvent. The DMF mixed solvent comprises, by weight, 70 to 98% of dimethyl formamide and 2 to 30% of acetonitrile, preferably, 80 to 95% of dimethyl formamide and 5 to 20% of acetonitrile; the mixed solvent is prepared by mixing dimethyl formamide and acetonitrile in proportion and functions as an extracting agent in separation of C5 fraction. The method comprises the steps of removal of light components, a dimerization reaction, pre-removal of heavy components, extractive distillation, resolving, refining, etc. According to the invention, the mixed solvent has enhanced selectivity, which enables the ratio of a stage number of an extractive distillation column to the solvent to be reduced and investment for equipment and operational cost to be lowered down.