Chlorophyll-a (Chla) can intuitively reflect the degree of eutrophication of water, Chla concentration can be accurately estimated via the three-band bio-optical model because it can weaken the influence of factors such as suspended and yellow matter in case-II waters. Therefore, the approximate position of the three-band factor was determined by analyzing the spectral characteristics of the measured water body. Further, three characteristic bands and a retrieval model were established using the exhaustive method and correlation analysis. Results show that when λ₁=661.63 nm, λ₂=693.54 nm, and λ₃=757.35 nm, the three-band factor [ Rrs-1(λ₁)- Rrs-1(λ₂)]R_rs(λ₃) exhibits a high correlation coefficient with the Chla concentration (r=0.830). The determination coefficient, root mean square error, and mean absolute percentage error of the model are 0.859, 2.446 mg·m ^-3, and 32.169%, respectively, furthermore, the accuracy is better than that of the band ratio and reflection peak models. These results can provide a theoretical basis and technical support for the Chla retrieval in the lower reaches of the Minjiang River and enable band selection for the subsequent retrieval of the Chla concentration in case-II waters using the three-band factor method.