The asymmetry and narrow linewidth properties of the Fano line shape are conducive to the realization of refractive-index sensing with high sensitivity and low detection limit. In this study, the coupled structure of the microring resonator and the Fabry-Perot cavity was designed based on the slot waveguide, using the three-dimensional time-domain finite-difference method. The Fano line shape resonance was realized and utilized to improve the performance of refractive index sensors. In contrast to reported complex structures such as multiple micro-ring cascades, a sensitivity of 500nm/RIU and detection limit of 4.00×10-5RIU were achieved under the wavelength tracking scheme based on the Fano lineshape resonance of the single-slot waveguide microring resonator. The sensitivity was 7.24×104dB/RIU for a detection limit of 5.52×10-6RIU under the intensity tracking scheme.