Abstract: Nano aluminum trihydroxide gels were prepared by carbonation in rotating packed bed under high gravity，then were subsequently modified by thermal hydrolysis in an agitated closed vessel to synthesize a novel nano-scale modified aluminum hydroxide powder with the beginning of thermal decomposition higher than 350℃ and weight loss of 51%. The mechanisms of carbonation and modification processes, as well as the influences of such factors as temperature, high gravity level, gas/liquid ratio, sodium aluminate concentration, final pH on carbonation and the influences of such factors as selection of precursors, temperature, modifier/ aluminum trihydroxide, aluminum trihydroxide concentration on modification were analyzed in detail. The modified product was formed by esterification and had ultra thin rhombic morphology of 20～40 nm in thickness, 100～200nm in length, and 50～100nm in width.