The invention discloses a method for the wide-range and high-resolution detection of a gas-liquid refractive index. The method includes the following steps: S1, inputting a sample to be detected intoa sample chamber; S2, allowing parallel lights emitted by a laser to enter a prism-coupled hollow metal-coated waveguide to excite surface plasma resonance; S3, calculating the refractive index rangeof the sample according to a surface plasma resonance attenuation total-reflection absorption peak received by an image sensor; S4, determining the angular position range of an ultrahigh-order guidedmode according to the refractive index range; S5, allowing the parallel lights emitted by the laser to enter prism-coupled hollow metal-coated waveguide and excite the surface plasma resonance in theangular position range; and S6, obtaining the matching angle of the ultrahigh-order guided mode according to the attenuation total-reflection absorption peak received by the image sensor in order to determine the refractive index of the sample. The method avoids the disadvantage of low resolution of an SPR technology, overcomes the miscalculation caused by too many modes in submillimeter-level hollow metal-coated waveguides, and achieves the wide-range and high-resolution detection of the refractive index.