The subwavelength dielectric grating-metal structure with a quartz glass substrate is proposed. It can be seen as a waveguide which is composed of metal layer, grating and superstrata according to the equivalent medium theory. With proper incident angles and light wavelengths, the total resonance absorption occurs. The resonance spectra of total absorption are analyzed using rigorous coupled-wave analysis (RCWA) method. The results show that the peak of TM1 mode of the waveguide is very sharp and sensitive to variation of refractivity of the superstrata. The angle sensitivity and wavelength sensitivity are 127.87\O /RIU and 409.35 nm/RIU, respectively, and the linearity between the resonance peaks and the refractivity of superstrata is good in a large range of refractive index of superstrata. Compared with guide-mode sensors of all dielectric and grating-type surface plasmon resonance sensors, the proposed structure can realize high sensitivity and the narrow resonance peaks can provide high detection precision.