Andalusite is one of the most important raw materials for alumina-silica refractories, exhibiting excellent alkali attack resistance due to its mullite-high silica glass phase structure after complete mullitization. However, the correlation of its mullitization process and alkali attack resistance has not been fully revealed. In this work, the mullitization process and microstructural evolution of andalusite with the size of 3~5 mm after firing at 1 450~1 600 ℃ for 3 h were investigated, and the alkali attack resistance behavior was evaluated according potassium vapor method. The results show that with the increase of calcining temperature, the andalusite on the surface and near the crack area transforms into mullite-high silica glass phase structure firstly, and then the transformation occurres inside gradually until completing mullitization. The alkali attack resistance behavior depends on the degree of mullitization. After calcining at 1 450 ℃, a thin layer of mullite-high silica glass phase composite structure is formed, and the main alkali attack process occurs directly between potassium vapor and andalusite, resulting in poor alkali attack resistance. After calcining at 1 500 ℃ and above, a mullite-high silica glass phase composite layer with a certain thickness is formed on the surface and near the large crack of andalusite. Potassium vapor and high silica glass phase firstly react to form potassium silicate liquid phase, and then the liquid phase produces erosion and dissolution on mullite phase, preventing the direct reaction erosion of alkali vapor on mullite. Thus, andalusite shows excellent alkali attack resistance.