In this research, we investigated the surface-wave dispersion characteristics in a grounded dielectric slab. Due to the phase match between the plane wave in a high dielectric constant medium and the surface wave supported in the grounded dielectric slab, the plane wave couples into the surface wave and is absorbed by the lossy substrate accordingly. By progressively changing the incident angle and operation frequency, the surface wave dispersion curves can be readily obtained by measuring the absorbance for the incident plane wave.