The ionization of F2 center in LiF and NaF crystals are explored in this paper. Experiments show that F+2 centers are created in LiF crystals with F2 center when they are irradiated by Hg-lamp, pulse Xe-lamp and D. 0. carbon arc. And F+2 centers are created in NaF crystals with F2 center when they are irradiated by pulse Xe-lamp and W-lamp. The problems about the efficiency of two-step ionization are discussed in the paper. The analysis shows that the way of increasing the efficiency is: it is necessary