Kinetics and mechanism of ammonia evaporation reaction of magnesium oxide using light burning magnesium powder and ammonium chloride as raw materials were studied.Results showed that when the reaction was carried out for 30 min，the concentration of magnesium ion in the solution was about 0.14 mol/L at 70~90 ℃，and the concentration was 0.5 mol/L at 100 ℃.XRD results showed that the magnesium oxide without forming Mg2+ in the ammonia evaporation reaction existed in the filter residue in the form of magnesium hydroxide.As the calcination temperature increased，the activation ener gy of the magnesium oxide hydration reaction increased gradually.When the calcination temperature was 600 ℃，the activa tion energy was 64.789 9 kJ/mol；when the calcination temperature was 800 ℃，the activation energy was 81.350 6 kJ/mol.When magnesium hydroxide and magnesium oxide were mixed in terms of different amount of substance ratios for the ammonia evaporation reaction，the rate of ammonia evaporation increased with the amount of magnesium hydroxide in the system increases.Ammonia evaporation reaction of magnesium oxide can be divided into two stages：In the first stage，magnesium ox ide is hydrated in the ammonium salt system to form magnesium hydroxide，and at the same time，part of the magnesium oxide and magnesium hydroxide react with ammonium chloride to form magnesium ions.In the second stage，finally the system completely became an ammonia evaporation system of magnesium hydroxide.