In the article the theory of auto localization rate of excitons is considered. With help of the graphs it was shown that in KI and RbI crystals with increasing temperature the rate of auto localization increases and decreases with increasing degree of compression at a fixed temperature. With use of the quantum- mechanical methods we were able calculate the lifetime of free excitons, the free run length of excitons before auto localization. We have analyzed that the lifetime of free excitons decreases in the sequence RbI, KCl, KI, KBr, NaBr, NaI, CsI. The results are in good agreement with experimental data and allow us to study the kinetics of luminescence decay and conditions of defect formation in alkali halide crystals.