DAF has been used to treat raw water with low temperature, low turbidity, high chroma or algae. In a DAF pilot, the removal path and mechanism of ammonia nitrogen were analyzed under different temperature. The results showed that the removal rates of total nitrogen and ammonia nitrogen were slightly reduced by air flotation under high temperature. When the temperature was low, the NO2-N of effluent would increase a little. The concentration of ammonia nitrogen in the scum layer could reach 2.74 mg/L, which was the main removal way. At high temperature, the volatilization rate of ammonia nitrogen was 2.8 times higher than that at low temperature. When the wind speed was 4.5 m/s, the volatilization rate could be significantly increase to 1.5 mgN/m2/d.