Fermi refractive-index distribution gradient waveguides are fabricated on the optical glass B270 using ion exchange process in the composite salt of 0.004AgNO3-0.996NaNO3. Absorption spectrum characteristics of the Fermi graded refractive index waveguide with an absorbent clad is theoretically analyzed. The experimental result about propagation loss of the waveguides is coincident with the analytic result. A testing waveguide circuit with a double-sample serial structure for measuring the liquid absorption loss is presented. The measured result shows that there is a remarkable linear relationship between solution concentration and refractive index's imaginary part which represents the feature of solution clad absorption, and the sensitivity is related to the modes and the parameters of waveguide, and particularly to the depth of waveguide. By using this sensing relationship, the concentrations C. I. Pigment Green7 solution samples 13 with kinds of different concentrations have been measured. The standard deviation between the measured values and the actual values is less than 0.07％.