In this study, roasted spent HDS ash (sHDSc-A) was used for the first time to catalytically pyrolyze oily spent HDS catalysts (sHDSc) to improve the yield and quality of pyrolysis oil. The results showed that sHDSc-A promoted the decomposition of coke in oily sHDSc, resulting in the recovery of more oil and gas. Meanwhile, sHDSc-A significantly improved the quality of the pyrolysis oil. They inhibited the aromatization of alkanes to increase the saturation of the pyrolysis oil from 59.39% to 74.25% and the H/C radio from 1.62 to 1.72; promoted the decomposition of long-chain alkanes to increase the content of C11–C22 from 41.97% to 61.99%; enhanced the conversion of carboxylic acids to ketones led to the reduction of heteroatomic compounds such as N (56.10%–45.39%), S (66.95%–56.59%), and O (45.26%–26.70%) in the pyrolysis oil. The promotion of sHDSc-A in the pyrolysis process is attributed to the catalytic effect of the metal oxides in sHDSc-A. Among them, Al₂O₃ and Fe₂O₃ can promote decarboxylation of carboxylic acids and reduce O mobility, while MoO₃ and Fe₂O₃ play a significant role in reducing coke and increasing pyrolysis oil. NiO can also promote methane vapor reforming, and thus increase the production of H₂ in non-condensable gas. This study achieves self-circulation of oily sHDSc with a “waste-treatment-waste” strategy that presents the advantage of value-added energy recovery and waste reuse.