According to the principle of the light attenuation due to absorption and scattering of both the excitation and the fluorescence lights in a deep sectional thick sample, the normalized fluorescence intensity expression is obtained for the light received by an optical system. The mathematical models of the iterative and FFT treatment methods are given. Using computer analog the FFT method is compared with the iterative one in two respects of numerical accuracy and computational efficiencies. Finally, the real image after restoration of the sectional sample is reconstructed by computer simulation with the FFT method.