In this paper, we use the amplification transfer function （ATF） to numerically calculate and analyze the spectral properties of parametric fluorescence （PF） via spontaneous parametric down-conversion. The results show that the output angle of single-wavelength PF which is nondegenerate is amplified and the whole spectrum of PF gradually becomes weak and has a continuous distribution. About the dense distribution of the broadband spectrum constituents near the degenerate state, we select two different pump pulses to numerically calculate it. With respect to the sensitive character of the phase-matching angle near the degenerate state, we use ATF and the spectrum probability distribution function （SPDC） to calculate and analysis it individually, the two results are consistent with each other.