Theoretical model of single backscattering spectra based on Mie scattering theory is established for a two-layer scattering media according to the structure characteristic of epithelium tissue. The theoretical model makes it possible to separate the singly backscattered light from the uppermost layer by subtracting the depolarised component from the backscattered light. The characteristic of scattering spectra is analysed by simulation calculation when the morphological parameters, including mean diameter, distribution and relatine refractive index, change. The influences of mean diameter, distribution and relative refractive index of the particles of the uppermost layer on the single backscattering spectra curve and its amplitude of wave components of different orders are further studied by Fourier waveform analysis method. The results show that the single backscattering spectra are sensitive to the mean size, distribution and relative refractive index of the particles, which show direct influences on the amplitude, frequency of the ripple structure of spectra and the wave components of different orders. The simulation results can be used to identify and extract the characteristic of precancerous scattering spectra.