Semiconductor-based surface-enhanced Raman spectroscopy (SERS) substrates with engineered defects have garnered significant research interest due to their comparable enhancement performance to traditional noble metal-based substrates. Among various defect engineering approaches, vacancy creation and elemental doping have emerged as two predominant strategies for optimizing semiconductor-based SERS substrates. Nevertheless, the mechanism and interplay between these two defect types in augmenting SERS enhancement have remained poorly elucidated in previous research. Herein, a type of dual defect synergistic boosted highly sensitive SERS substrate based on nanostructured CrxTiyO2 with a rational design of Ti vacancies and Cr doping is proposed where Ti vacancies induce electron spin polarization, while Cr doping generates a midgap doping level. The optimal Crx3TiyO2 substrate achieved remarkable detectability of 10−11 M (mol/L) and 10−8 M for methylene blue (MB, 1.86 eV of energy gap) and 4-mercaptobenzoic acid (4-MBA, 4.63 eV of energy gap), respectively, alongside excellent reproducibility and stability. It is proposed that the dual defect Crx3TiyO2 synergistically optimizes the band structure and enhances carrier separation efficiency, thus effectively promoting the photoinduced charge transfer process between the substrate and molecules enabling superior signal amplification, which is confirmed by the density of states using DFT calculations. More importantly, this work offers a novel pathway for designing high-performance semiconductor-based SERS substrates through regulating the multidefect synergy.