Abstract: Basing on ion migration in xide films, a original method named IMM（Ion Migration Method） has been established to characterize the micro-defects in oxide films quantitatively. Several kinds of zircaloy oxide films formed at different corrosion conditions, were measured by IMM. On the basis of the results, it is concluded that IMM can distinguish the micro-defect difference between the different samples and the micro-defects evolution during the corrosion sensitively. After IMM has been further improved, it will be a effective method to analyse the microstructure of oxide films.