The invention relates to a method for preparing a substrate material with a multilayer composite protective film, which comprises the following steps: putting the substrate material into a
reaction chamber, and heating the substrate material until the temperature thereof is 100 to 500 DEG C; introducing trimethyl aluminum or Al (CH3) N (CH2) 5CH3 precursor into the
reaction chamber within 0.2 to 0.5 seconds under the pressure of 0.1 to 10
Torr; introducing
nitrogen or
inert gas into the
reaction chamber so as to remove the trimethyl aluminum or Al (CH3) N (CH2) 5CH3 residual gas which is not subjected to
chemisorption by a substrate; under the pressure of 0.1 to 10
Torr, introducing
ozone or vapor
reactive gas into the reaction chamber within 0.2 to 0.5 seconds so as to deposit an
alumina atom layer on the substrate, wherein the thickness of the
alumina atom layer on the substrate is 2 to 100nm; and replacing the trimethyl aluminum or Al (CH3) N (CH2) 5CH3 precursor by using
chlorosilane,
hexachlorodisilane or
tetraethyl orthosilicate as
silicon source, then repeating the steps above, and covering a
silicon dioxide layer on an
alumina layer, wherein the thickness of the alumina layer is 2 to 100nm; and finally, obtaining the substrate material with a composite inorganic protective film in a Al2O3 / SiO2 double-layer structure, wherein the thickness of the substrate material is 5 to 120nm. The method can precisely control the thickness of the film, wherein the thickness of the film can directly and precisely be controlled within a range of 1 to 100nm, and the film has excellent
oxidation resistance and gas
permeation resistance, and can control the ratio of Al2O3 to SiO2.