ABox abduction is the foundation of abductive reasoning in description logics. It finds the minimal sets of ABox axioms which could be added to a background knowledge base to enforce the entailment of certain ABox assertions. In this paper, an abductive reasoning algorithm for the description logic ALCI is presented. The algorithm is an extension of an existing ABox abduction algorithm for the description logic ALC, with the feature that it is based on the Tableau of ALCI directly and do not need to use arguments and Skolem terms. It firstly transforms the ABox abduction problem into the consistency problem of knowledge base; then traditional Tableau construction process for ALCI is expanded to deal with this problem; finally the solution of the abduction problem is constructed by a process of backtracking.