To enhance the acid soil improvement performance of vermicompost, this study developed two vermicompost-based acid soil conditioners, B+M+V and BMV, by incorporating high-alkalinity substances—oyster shell powder (M) and biochar (B) into vermicompost (V) through physical mixing and vermicomposting. A pot experiment was conducted to compare the application effects of B+M+V, BMV, and other amendments such as lime (L), oyster shell powder (M), biochar (B), and vermicompost (V). Results indicated that L and M had the most pronounced soil acid reduction effects, with soil pH increasing by 3.18 and 2.81 units, respectively, and soil aicd-base buffering capacity (pHBC) increasing by 196.81% and 236.97%, respectively. The acid reduction effects of the B+M+V and BMV conditioners were second best, with soil pH increasing by 1.35 and 1.49 units, and pHBC increasing by 124.97% and 104.07%, respectively. Applications of B and V showed limited effects on soil acid reduction. The application of V, B+M+V, and BMV significantly improved soil fertility. Specifically, soil organic matter increased by 197.53% and 222.51% with B+M+V and BMV applications, respectively. Additionally, soil available phosphorus, potassium content, and cation exchange capacity (CEC) were significantly improved by B+M+V and BMV applications. The plant height and biomass of Shanghaiqing were significantly higher with B+M+V and BMV applications compared to L, M and B applications. Moreover, the accumulated absorption of nitrogen, phosphorus, and potassium by Shanghaiqing were significantly increased with B+M+V and BMV applications. Principal component analysis evaluation revealed that L and M excelled at soil acid reduction, V, B+M+V, and BMV were good at improving soil fertility, while B+M+V and BMV were effective in promoting plant growth. Overall, B+M+V and BMV demonstrated the best comprehensive effects on acid soil improvement. The above results indicated that the two types of vermicompost-based acid soil conditioners effectively combined the advantages of pure vermicompost in soil fertility improvement and the strong acid reduction capacity of high-alkalinity substances, and could play an excellent comprehensive role in acid soil improvement.