This paper studied the oxidative degradation of the dye eosin by the combined effect of ferrate and light, mainly investigated the effects of light intensity, reaction temperature, amount of ferrate added, initial concentration of eosin etc. on the degradation rate of dyes, and tried to explore the degradation mechanism of the dye. The study found that light and ferrate have a synergy effect on the oxidative degradation of dyes. Increasing the light intensity and increasing the amount of ferrate added can significantly increase the removal rate of eosin; the influence of reaction temperature and initial concentration of eosin on the final eosin removal rate is complicated, and there are optimal reaction temperature and the initial concentration of eosin. By studying the UV-visible absorption curves of eosin at different time during the degradation reaction, it can be found that no new product formed during the reaction. It is inferred that the eosin is eventually oxidized into smaller molecules such as carbon dioxide and water.