The microchannel plate (MCP) ion barrier film's stopping function on incident positive ions in the third generation low-level-light imaging tube was introduced. The concepts of nuclear stopping power

electronic stopping power and average range were also introduced

the micrographs of unfilmed MCP and MCPs filmed with different thicknesses were shown. Using Tomas-Fermi shielding potential

we analyze and discuss this problem and a Monte-Carlo simulation was peromed. Analytical expressions and corresponding nuclear and electronic stopping power curves have been shown. Quantitative results were given

reflecting the stopping function of Al

2

O

3

and SiO

2

films when nucleus and electrons impinge perpendicularly with different energies. Table 1~3 show the corresponding technical data. The conclusion is that the stopping power of Al

2

O

3

film is stronger than that of SiO

2

and the selection of Al

2

O

3

ion barrier film is reasonable and feasible. After the theoretical analysis and experimental simulation

the conclusions are brought forward as follows:The stopping function of ion barrier film on the incident ions can be described by two concepts of nuclear stopping power and electronic stopping power. When the thickness of the films is constant

the range of the ions with the same energy in Al

2

O

3

films is two to three times as short as that in SiO

2

films. It is indicated that the capability of the stopping function of Al

2

O

3

films is higher than that of SiO

2

films. From the calculated results of the stopping function of the films on the ions

it is obviously concluded that the capability of nuclear stopping function on the ions is higher than that of electron

which is in agreement with LSStheory. When 9999 oxygen ions with the energies of 100

300

500 eV are perpendicularly incident to the Al

2

O

3

film with 5 nm thickness

no transmitting ions are observed. While in the same conditions

34 and 629 oxygen ions with the energies of 300 eVand 500 eV

respectively

can pass through the SiO

2

films with 5 nm thickness

i.e

. the maximal transmittance is 6%. In brief

the capability of the stopping function of Al

2

O

3

films is higher than that of SiO

2

films

resulting from that Al

2

O

3

films are high density and the fiber rigidity of Al

2

O

3

films is close to that of corundum; while SiO

2

is atom crystal

and the rigidity of SiO

2

films is equivalent to that of crystal and inferior to that of Al

2

O

3

.