A new alkali dissolution method is used to extract aluminum hydroxide from high-alumina fly ash in this study. The first step alkali dissolution is to obtain desiliconized fly ash with relatively high Al₂O₃/SiO₂ ratio. The amorphous silica in the fly ash is partly leached when the fly ash is leached with 8 mol/L sodium hydroxide solution at 95℃. The desiliconized fly ash is then used for the second step alkali dissolution as the material. The desiliconized fly ash mixed with CaO are leached with 18～20 mol/L sodium hydroxide solution at 260～280℃ and the dissolution efficiency of Al₂O₃ reaches 85%. Then reduced causticity ratio, deep desilication and carbonation decomposition are carried out on the basis of acquired sodium aluminate solution. The features of the prepared product of aluminum hydroxide are determined by XRD, SEM and chemical analysis. The results show that the aluminum hydroxide has fine crystal and slight particle aggregate sphere 70～80μm in diameter. The product can satisfy Class 1 of the China National Chemical Standard GB/T4294-1997. Compared with other technologies, this technology can avoid high temperature sintering procedure and realize low energy consumption, and the process is quite consistent with the environment protection idea.