Chlorophyll-a is one of the main water color elements which affect inland water optical properties, and it is the important parameter reflecting water eutrophic level. In the recent years, many methods and models are developed to retrieve Chl.a concentration. These methods or models all uses immobile bands. However, characteristic bands of chlorophyll-a move with the concentration changes. Especially, phenomenon of red-shift effect occurs obviously at 701nm reflective peak. As a result, using immobile bands to retrieve Chl.a concentration must bring some errors. In order to obtain higher precision, author in this article analyzed water spectra with different Chl.a concentrations and brings forward a new method of using dynamic apex to retrieve the Chl.a concentrations.