The emergence of structured light as a controllable photonic entity has transformed the manipulation of electromagnetic fields, facilitating advanced light-matter interactions that critically enhance the operational efficiency of diverse fiber-optic sensors. Within this emergent framework, the Airy-Bessel beam, characterized by its non-diffracting propagation and self-healing dynamics, stands as a paradigmatically superior candidate for fiber-based refractive-index measurements. In this investigation, we employed the Airy-Bessel excitation within a decladded multimode fiber to transcend the inherent constraints of conventional Gaussian illumination, whose efficacy is typically curtailed by shallow evanescent-field penetration and diminished mode-medium interaction. By tailoring the excitation conditions, higher-order guided modes are efficiently stimulated, thereby amplifying the evanescent-wave contribution and enabling a superior refractive index sensitivity. The proposed sensor architecture was validated using full-vector beam propagation method (BPM) numerical modeling performed in OptiBPM (v13.1.3, Optiwave Inc.), allowing a comprehensive analysis of Airy-Bessel beam evolution within the sensing structure. The sensor demonstrates absolute sensitivities of 1502.96 dB/RIU and 1878.72 dB/RIU for sensing lengths of 20 cm and 25 cm, respectively, with corresponding detection resolutions of 6.65 × 10−6 RIU and 5.32 × 10−6 RIU. These results affirm a notable advancement over Gaussian beam configurations and highlight that structured-beam excitation enables scalable sensing without the need for geometric alterations such as tapering, side-polishing, U-bending, surface-functionalized designs, etc. Therefore, the proposed sensing method furnishes a potent pathway for futuristic fiber-optic sensing across chemical, biomedical, and environmental domains where ultralow refractive index detection is imperative.