Abstract: The effect of ultrasonic treatment on the unit structure of pre-and post-hydrotreating asphaltenes were investigated with Shengli vacuum residue and Saudi Arabia light vacuum residue as raw materials. The unit molecular structures of the asphaltenes were analyzed through simulation with the software Chem Bio Draw Ultra version 2012, combining with the data of ¹H-NMR, FT-IR and structural parameters of asphaltene units. The results showed that the association number is decreased by ultrasonic treatment, as it can reinforce the ring opening and desorption of alkyl side chain of the asphaltene unit and then exhibits a significant influence on the structure of asphaltene unit after hydrotreating. The model used here can vividly reflect the influence of ultrasonic treatment on the chemical structure of pre-and post-hydrotreating asphaltene unit at molecular level.