<p>This study focuses on the composition characteristics of coal tar, which is rich in aromatic hydrocarbons, and employs long-chain olefins as alkylating agents for directional modification of molecular groups. Gas chromatography–mass spectrometry was used as the primary analytical technique. The optimal process conditions for the alkylation reaction were investigated. Experiments were conducted on the alkylation of light fractions to analyze the component migration law during the alkylation of coal tar fractions, as well as on the alkylation of hydrogenated heavy fractions to examine the effect of hydrogenation pretreatment on the alkylation reaction. Finally, a preliminary performance evaluation of the products from each fraction was carried out. The results indicate that the optimal process conditions for the alkylation reaction are as follows: using AlCl₃ as the catalyst, a reaction temperature of 100&#xa0;°C, and a reaction time of 3&#xa0;h. The main substances undergoing alkylation in each coal tar fraction were identified as monocyclic aromatics containing hydroxyl groups and a small amount of bicyclic aromatics. Meanwhile, hydrogenation pretreatment was found to inhibit the alkylation reaction, primarily because the hydrogenation process removes hydroxyl groups from the aromatic rings, reducing the reactivity of the substrates, and because compounds such as tetralin generated during hydrogenation promote hydrogen transfer, leading to the saturation of olefins. The performance evaluation results show that key indicators, such as the viscosity of the products from each fraction, were significantly improved, demonstrating promising potential for industrial application.</p>