The samples of BaF

2-x

Cl

x

and BaFCl:Eu

2+

are prepared.It is proved that F centers and V

k

(Cl

2

-

)centers exist in the X-irradiated BaF

2-x

Cl

x

by the technique of electron spin resonance.The valent state of Eu

2+

in BaFCl:Eu

2+

does not change under Xirradiation and unirradiation.From above

the process of X-ray storage is advanced

after X-ray irradiate the sample of BaFCl:Eu

2+

free electrons and holes are formed in it.The electrons are trapped in two chlorine ions to form V

k

(Cl

2

-

)centers.The VK(Cl

2

-

)centers migrate nearby Eu

2+

and finally become the stable V

k

(Cl

2

-

)centers.