Experimental study on the stability of F2+ centers in oxygen doped LiF crystals is reported. The mechanism on the decay and stabilization by O of F2+ centres are discussed in detail. Experiments show that the decay process of F2+ centers in LiF is a second order reaction. The measurements of rate constants and activation energy of F2+ center decay in the range of room temperature indicate that the activation energy increases by about 0.2 eV and the rate constants decrease appreciably in oxygen doped LiF compared with the undoped crystals. A theoretical estimation of the difference of binding energy and that of electron affinity of F2+ centers between doped and undoped LiF crystals is also given briefly.