Aiming at the problem of narrow dynamic range when microring resonators are used for refractive index sensing, this paper proposes a refractive index sensing technology based on few-mode silicon nitride micro-ring resonators, which enables the calculation of resonance wavelength drift without considering the original reference value and increase the refractive index detection range, and verify that higher-order modes are more sensitive to environmental changes. After theoretical analysis, a simulation model is established to verify the feasibility of the method, and the sensing experiment is carried out with the solution to be tested with different refractive index. Finally, the refractive index sensitivity of 91.79 nm/RIU and the resolution of 10-5 RIU are obtained.