So far, Estimation of the number of reserved stopes in underground mining has only been carried out based on empirical methods. Not any accurate criteria have normally been employed in these methods. Thus, the confidence level for substituting the reserved stopes instead of failed stopes, so that the mine production is continued, is not predictable.In this paper, a new method is presented to compute the confidence level for continuation of mine production. This method is based on the assumptions of knowing the number of the main stopes, the probability of the failure of the active stopes and the probability of repairing the failed stopes. In this method, the main and the reserved stopes are modeled, and then applying the Markov chains, the probability of using the reserved stopes during the mine production period is estimated.