The maximum entropy approach is one of the most important threshold selection methods in image processing.Many researchers avoid the problem of computationally prohibitive when the maximum entropy criterion is applied to multi-level threshold selection.This paper proposes to deal with this problem using ICM (iterated conditional modes) algorithm.Comparing the ICM algorithm with the simulated annealing algorithm proposed by H.D.Cheng et al,the experimental results show the effectiveness of ICM algorithm fully.