The quantitative relationship between Spectral Reflectance (SR) characteristics of water and chlorophyll-a( Chi. a) concentration in Lake Taihu was analysed based on the in-situ data collected by ASD FieldSpec Hand-Held Spectroradiometer. The results reveal that the Chi. a concentration can be quantitative retrieved using SR at wavelength of 720 nm，or using the ratio of SR at wavelength of 806 nm and 507 nm. The model using SR at wavelength of 720 nm is an effective retrieval model whether Chi. a concentration > 10ug/L or Chi. a concentration < 10 ug/L, while the model using the ratio only retrieve Chi. a concentration effectively for Chi. a concentration < 10ug/L. It was found that there is high correlation between Chi. a and the first derivative at 690 nm, also high correlation between Chi. a and the second derivative at 702 nm through spectral derivative method，but the model retrieve accuracy using the first derivative or the second derivative is not significantly improved compared to the model directly using SR. But the retrieval accuracy using the second derivative is a little higher than the model using the first derivative. So it was concluded that the Chi. a Concentration in Lake Taihu can be retrieved using SR at wavelength 720.