By using the method of multi-peak Gaussian fitting,the fluorescence spe ctra of serum from 5-15days of liver cancer mice were studied,and the results show that with the growth of tumor,the peak position of the fluorescence composing line and its Gaussian func tion move to short wave direction. Based on the theory of molecular vibration,it is believed that in the course of tumor growth,the content of some luminous molecules in the serum increases, the molecules tend to be close to each other,the interaction between the molecules is enhanced,the chem ical bond between the atoms tends to elongate,and the vibrational energy level of the atomic state is reduced. If the lowest vibrational level of the first electron excitation state is not changed,the ene rgy difference between the ground state and the lowest vibrational level of the first electron excited stat es tends to increase,resulting in the peak position of the correlated fluorescence spectral curve becoming blue shift. The results of this study show that the nonlinear multi-peak fitting and molecular vibration analys is of serum fluorescence spectra are helpful to reveal the deep-seated causes of the changes of fluoresc ent substances in serum from the molecular level.