NOVELTY - Purifying eutrophicated water using combination technology of micro-bubble air-flotation and biological contact oxidation involves mixing the mixture having micro-bubble and polluted water into polluted pool, denitrogenating the mixture to obtain mixed thalli having nitrobacteria, nitrosobacteria and denitrifier, mixing the algae, micro particle suspension and water soluble contamination in pool to release contaminants as vapor, and finally degrading mixture floating in the water-surface by microorganism to discharge contaminants as gas molecule in atmosphere.    USE - The method is useful for purifying eutrophicated water (claimed).    ADVANTAGE - The method has desired efficacy.    DETAILED DESCRIPTION - Purifying eutrophicated water using combination technology of micro-bubble air-flotation and biological contact oxidation involves directing the polluted water fetched from the sealed polluted water body (lakes and pools) into the micro-bubble generator to form the mixture having micro-bubble and polluted water, mixing the mixture into polluted pool using flow-directing pipe, where the gas-water mixture spraying open of the micro-bubble generator is installed on the bottom of the water, the biological reactor filled with inappropriate stuffing is installed on the spraying open, and the water-fetching open of the micro-bubble generator is installed on the position distant from the spraying open while operating the device, denitrogenating the mixture using biological reactor to obtain mixed thalli having nitrobacteria, nitrosobacteria and denitrifier, mixing the mixture generated by micro-bubble generator and water to integrate the algae, micro particle suspension and water soluble contamination, releasing the contaminants in the form of vapor during the upwards floating process, and finally degrading the mixture floating in the water-surface by microorganism in the biological reactor at the pollution region to discharge contaminants as gas molecule in the atmosphere.