Commercial high purity corundum brick, corundum-mullite brick, mullite brick, calcium hexaaluminate brick and calcium hexaaluminate-corundum brick were studied to investigate their reaction state and alkali vapor corrosion mechanism at 1 370 and 1 500 ℃. The results show that: (1) served in hot alkali vapor, the high-purity corundum brick has no obvious slag layer but expands dramatically; (2) the corundum-mullite brick shows obvious reactive expansion at 1 370 ℃ and melting corrosion happens at 1 500 ℃; (3) at 1 370 ℃, alkali vapor and mullite brick react and form a slag layer without volume effect; when the temperature increases to 1 500 ℃, the reaction melting corrosion intensifies; (4) the calcium hexaaluminate brick and the calcium hexaaluminate-corundum brick form a thin slag layer in alkali vapor, and the sample surface absorbs Na+ to form a dense layer with small volume effect.