In order to study the autofluorescence spectral changes during cancer cell cycle, the autofluorescence spectrum of synchronically cultured HeLa cell in the G1, S, G2 and M portions of the cell cycle is measured. The results show that there is autofluorescence phenomenon during the cell cycle and the fluorescence intensity in each stage is different. The fluorescence sptectrum exhibits the characteristic peaks at 360 nm and 680 nm. The changes of fluorescent molecules (such as aromatic amino acid and porphyrin) in HeLa cells during the cell cycle result in these differences. The fluorescence spectra of different stages reflect the changes of aromatic amino acid and porphyrin in cell during the cell cycle and can be utilized to study the state of the cancer cell cycle.