Abstract: The water treatment effect of a protein skimmer with different ozone concentrations for recirculation system of industrial fish farming was studied in this paper. Foam separation principle and ammonia nitrogen removing theory of the protein skimmer was described. A protein skimmer with a discharge of 50 m^3?h^-1 was designed. The skimmer was used in a recirculation system, and relative water quality parameters：protein, ammonia nitrogen, nitrite, nitrate, organic nitrogen, suspended solid, dissolved oxygen, were tested. The results showed that the egesta of the fish reared and the feedstuff residual could be removed efficiently. The removal efficiency of ammonia nitrogen and protein in the recirculation system was very high by entering ozone into the protein skimmer. The removal rate of protein, ammonia nitrogen, nitrite, nitrate, organic nitrogen, suspended solid were various along with the different ozone concentrations. And the dissolved oxygen was greatly increased.