Abstract: A on-line all optical-fiber fluorescence spectrum measuring system which can simultaneously measure Chlorophyll-a and b fluorescence spectrum in alga is introduced. Since wavelet transform can decompose signals into localized contributions of different frequency, it is applied to the technology of optical fiber and fluorescence methods to measure and to smooth the fluorescence spectrum of alga contained Chlorophyll-a and Chlorophyll-b. On this condition, the overlapping fluorescent peaks was resolved. It has the advantages of minitype,simple structure,passive sensing head, little spectral deformation, simultaneous multi-parameter measurement. It has been testified that this method is practicable.