Abstract: The fraction above 220℃ separated by rectification from the by-product C9 aromatic hydrocarbon fraction of ethylene cracking blends was mixed with solvent oil at a prescribed ratio，and dark petroleum resin can be produced by free radical polymerization reaction at a specific temperature and pressure. Reaction temperature，reaction pressure，and modifying agent content affected the softening point，viscosity and n-heptane value of the resulting resin and the process conditions of temperature，pressure and constant temperature time of thermal polymerization for producing dark petroleum resin were determined.