This paper focus on theory of diffusion-controlled annealing of the most mobile radiation-induced defects—I centers—in KCl crystals. The kinetics of annealing of pairs of close oppositely charged defects—α-I centers (arising as a result of the tunnelling recombination of primary Frenkel defects—F and H centers) and F-I centers (when H center trap electrons) is calculated taking into account defect diffusion and Coulomb/elastic interaction. Special attention is paid to the conditions under which multi-stage annealing arises; theoretical results are compared with the relevant experimental data.