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Due to the overlap of absorption and scattering of water constituents of case 2 waters, the retrieval precision of chlorophyll-a concentration is challenging. In this article, the absorption coefficient and backscattering coefficient of waters with different chlorophyll-a concentration were calculated after the absorption and back-scattering coefficients of special water constituents were measured. Afterwards, the above-water reflectance of remote sensing was achieved according to the radiation transfer model and the light-field distribution function of interface between the water and atmosphere. Based on the spectral characteristics of chlorophyll-a in red band region, two absorption boughs (Rrs674 and Rrs740) adjacent to reflectance peak were used to calculate the normalized peak area (NPA). After the relationship between the NPA and the chlorophyll-a concentration was studied, we concluded that there was a better relationship (R2=0.99) and lower RMS error (RMSE=5.09μg·L-1) than other retrieval models of chlorophyll-a. The retrieval model of NPA (C = a × NPAb + c, where C is the concentration of water constituents; a, b and c are the empirical parameters) has a promising prospect and could be used to retrieve the concentrations of water constituents with higher precision in accordance with the characteristics of various water constituents at different bands.