SiO

2

sol sealing agent was prepared from tetraethoxysilane（TEOS）by ethyl alcohol as solvent and hydrochloric acid as catalyst.The Fourier transformed infrared spectrometry（FTIR）contains dilation flutter absorption peak of S-O-Si

which shows the presence of SiO

2

particle in solution.The sealing agent has a great stability at elevated uemperature because the strength of dilation flutter absorption peak of Si-O-Si does not change with heat treatment temperature.It could be observed that the SiO

2

sol sealing agent fills up the hole of micro-arc oxidation coating on magnesium alloy.The corrosion rate of MAO coating sealed by SiO

2

sol can be reduced from 106mg/（m2·h）to 32 mg/（m2·h）.Moreover the anti-oxidizing performance of MAO coating at 410 ℃ is greatly improved by sealing

and the coating sealed by SiO

2

sol offers the effective protection for magnesium alloy substrate.