RVR and FCCS were employed as raw materials, modified with ET, high?quality coated asphalt products were obtained through optimization of the preparation process. The raw materials and products were characterized using FT?IR, XRD and TG/DTG. Combined with the information from 1H?NMR, elemental analysis, and molecular weight determination, the reaction mechanism was proposed. The results show that the difficulty of blending and modifying the raw materials is significantly related to the content of asphaltenes and aromatics, higher proportions of asphaltenes and aromatics facilitate the modification process. From the perspective of the reaction mechanism, the ⁺CH?CH {}_{\mathrm{2}}^{+} generated by the dehydration of ethylene glycol under acidic conditions plays a bridging role, enabling RVR, FCCS, and ET to form coated asphalts E?FCCS and E?RVR with condensed aromatic structures through polycondensation reactions. A higher content of aliphatic chain alkyl structures in the modified feedstock oil leads to stronger reaction activity. During the catalytic cross?linking polymerization process, these structures are prone to cleavage to form small molecules. These small molecules hinder the polycondensation reaction between polycyclic aromatic hydrocarbons, inhibit the increase in aromaticity of the system, and thereby interfere with the growth of graphite crystal structures, which is unfavorable for the formation of ideal graphite crystals with condensed aromatic hydrocarbons as basic units. The characterization and analysis results of the coated asphalts E?FCCS and E?RVR support this conclusion. By clarifying the intrinsic relationships between raw material structure, reaction mechanism, and product properties, this study provides theoretical and technical foundations for the preparation of coated asphalt via blending modification and catalytic polymerization of heavy oil.