The invention relates to a method for enhancing sludge air flotation concentration decrement and harmlessness by using high-concentration ozone, which comprises the following steps: mixing sludge and an air flotation concentration medicament, feeding the mixture into a pressure container tank through a gas-liquid mixing pump, generating micro-nano bubbles by ozone through a micro-nano bubble generating unit, feeding the micro-nano bubbles into the pressure container tank through the gas-liquid mixing pump, and discharging the micro-nano bubbles. Uniformly mixing the sludge, the air flotation concentration medicament and the high-concentration ozone; pumping the mixed solution into an air floatation contact chamber, and after air floatation, opening a slag scraping plate to remove floating concentrated sludge; all the concentrated sludge floats upwards and is discharged through a sludge outlet after being removed by a slag scraping plate, and sludge supernate after air floatation is disinfected and then is discharged through a concentrated water outlet guide pipe as bottom effluent. On the premise of greatly reducing the consumption of ozone, the water content of the concentrated sludge is quickly increased to 90-92%, the air flotation concentration efficiency is greatly improved, most antibiotic pollutants and pathogenic bacteria in the supernate are removed, the chromaticity of the supernate is reduced, and sludge reduction and harmlessness are remarkably enhanced.