Abstract：The autofluorescence spectra of human serum excited by lights of 457.9, 476.5, 488.0,501.7 and 514.5nm were measured ; And their characteristics and mechanism were also analyzed. The results of experiment and analysis indicate that there are two obvious fluorescent peaks and a weak one at 518, 640 and 590nm in the range of 500nm to 750nm, respectively, and these fluorescent peaks maybe mainly arise from contributions of bilirubin, riboflavin and its derivatives, (-carotene, zinc protoporphyrin , protoporphyrin IX and so on in human serum. The result will provide some reference for choosing Ar+ laser wavelength in the technique of spectra diagnosis.