In this work, a novel ultrasonic-assisted thermal cracking method for improving the yield of light oil from the thermal cracking of Huizhou atmospheric residue (HAR) is proposed and demonstrated. To achieve this, a self-developed autoclave ultrasonic reactor (20 kHz; 200 W) was designed. Gas chromatography (GC), and elemental analyser (EA) were employed to analyse the composition of gaseous and liquid products after the cracking of residual oil. Compared to the traditional thermal cracking process under similar conditions (430 °C; 8 MPa; 2 h), the ultrasonic-based process produced lower gas products (ca. 0.6%), higher gasoline and diesel fractions (ca. 10%), vacuum residue, and lower yield of coke yield (ca. 4%). In addition, coke produced by the ultrasonic-assisted thermal cracking method exhibited spherical morphology with narrow size distribution and smooth surface with small amounts of adsorbents attached to it. The derivative characteristic peak (101 crystal face) at 2θ of 43.56° belonged to α-graphite. The abnormal high local temperature and pressure conditions produced by ultrasonication were the key factors for the thermal cracking of residual oil. The experimental results indicated that the ultrasonic-assisted thermal cracking can dramatically lead to higher yield of light oil, higher degree of cleavage, and more favourable reactions under the same conditions (as those of traditional thermal cracking). Therefore, compared to the traditional delayed coking process, the proposed ultrasonic-assisted technology can significantly decrease the power consumption. This study has vital significance in predicting and enhancing the performance of thermal cracking on a large scale.