The concentration of chlorophyll a in inland water determines the plankton content, which is a main index to measure the eutrophication degree of water, and is also one of the important factors affecting the apparent reflectance spectrum of water. The three-band bio-optical model can effectively reduce the influence of suspended matter and chemical substances in Class II water during the inversion process and accurately estimate the concentration of chlorophyll a. Taking Baiyangdian Lake in Xiongan New Area, China, as the research area, the spectral characteristics of water were analyzed by using the measured water spectrum and chlorophyll a concentration, the position of three-band factors was determined by using the exhaustive method, the three-band inversion model was established and the accuracy was verified, and finally the results wreanalyzed and evaluated. The results show that at ${\lambda }_{\mathrm{1}}=\mathrm{673}$ nm, ${\lambda }_{\mathrm{2}}=\mathrm{729}$ nm, ${\lambda }_{\mathrm{3}}=\mathrm{782}$ nm, the maximum correlation coefficient between the inversion factors of the three-band model $[{R_{\mathrm{r}\mathrm{s}}}^{-\mathrm{1}}\left(\mathrm{673}\right)-{R_{\mathrm{r}\mathrm{s}}}^{-\mathrm{1}}\left(\mathrm{729}\right)]R_{\mathrm{r}\mathrm{s}}\left(\mathrm{782}\right)$ and chlorophyll aconcentration is 0.82. The determination coefficient, root mean square error, mean absolute error and mean relative error of the model are 0.67, 3.61 μg/L, 2.86 μg/L and 26.06%, respectively, indicating that for the water with high suspended matter and chemical substances, the three-band model has a good inversion accuracy compared with the wave segment ratio and single-band model. This study provides a certain theoretical basis and technical support for the inversion of chlorophyll a concentration in Baiyangdian Lake, which is helpful for the continuous monitoring of water quality in Baiyangdian Lake, and also provides an algorithmic support for the inversion of chlorophyll a concentration in Class II water using three-band model in the future.