Abstract: In virtue of stochastic autocorrelation function description of the impurity scattering potential in non-dissoluble magnetic-nonmagnetic granular films, we find a relationship between the resistivity of system and the size of gruanules. Furthermore, by introducing a phenomenological factor to account for the increase of correlation length caused by the external magnetic field, we get an analytical ex-pression for the giant magnetoresistance coffiecient. The calculations show that our theory agrees qualitatively with the experimental results.