Carbonation decomposition of hydrogarnet is a significant reaction of the calcification-carbonation new method for alumina production by using low-grade bauxite.In this work,non-isothermal decomposition kinetics of hydrogarnet in sodium carbonate solution was studied by high-pressure differential scanning calorimetry（HPDSC） at different heating rates of 2,5,8,10,15 and 20 K·min^-1,respectively.The activation energy（E_α） was calculated with the help of isoconversional method（model-free）,and the reaction mechanism was determined by the differential equation method.The calculated activation energy of this reaction was 115.66 kJ·mol^-1.Furthermore,the mechanism for decomposition reaction is Avrami-Erofeev（n=1.5）,and the decomposition process is diffusion-controlled.