This study proposes a photonic crystal nanobeam (PCN) side-coupling aperture chirped photonic crystal nanobeam cavity (PCNC) structure based on the Fano resonance principle. The Fano resonance can be realized by the destructive interference between the wide continuous state produced by the PCN structure and narrow discrete state generated by the PCNC structure. The generation mechanism of Fano resonance in the structure is qualitatively analyzed via the coupled mode theory, and the structure is simulated by using the finite-difference time-domain method. After quantitatively studying the influences of the structural parameters on the refractive-index sensing characteristics of the system, the structural parameters are optimized. Results show that the optimized figure of merit is as high as 5.1×10 ³, providing an effective theoretical reference and technical guidance for the design of integrated photonic-crystal waveguide sensors.