Abstract: Amorphous SiO₂-Al₂O₃ composite powder with high thermal stability was prepared by two-step calcination method. Firstly, amorphous Al₂O₃ precursor was prepared by mixed calcination of ammonium aluminum sulfate dodecahydrate and glucose, and then appropriate SiO₂ was introduced into amorphous Al₂O₃ in the form of ethyl orthosilicate. Amorphous SiO₂-Al₂O₃ composite powder with high thermal stability can be obtained after calcination. When SiO₂ introduction mass fraction is 26%, the powder remains amorphous structure after 4 h calcination at 950 ℃. After wet grinding of precursor, the thermal stability of the powder is further improved, and the powder remains amorphous structure after 4 h calcination at 1020 ℃. The results show that the amount of SiO₂ and the mixing uniformity of precursors have obvious effects on the high temperature thermal stability of the composite powders.