A method based on reflective mesoscopic spectroscopy for characterization of refractive-index fluctuations at nano-scale is introduced. Mechanism of mesoscopic spectroscopy for perceiving reflective-index fluctuations at length scale of nanometers is revealed. Based on simulation by finite difference time domain method, light propagation in one-dimensional refractive-index variable medium and resulting reflective spectral characteristics are analyzed. Through precise control of standard deviation and spatial correlation length of refractive-index fluctuations along one-dimensional channel, simulated disorder strengths and their relation to theoretical settings are quantitatively analyzed. Results show that reflective spectrum is highly sensitive to disorder strength and thus it is feasible for the refractive index fluctuations at nano-scale within one-dimensional channel to be perceived through reflective spectrum. Under certain approximating conditions, disorder strength is proportionally enlarged with increasing variance and spatial correlation length describing refractive-index fluctuations. The proposed method might be useful in probing statistical structural changes at nano-scale which are unperceivable up to now, and hence avoiding the limitation due to optical diffraction in far field.