Abduction is an important research work in AI(artificial intelligence)，and can be applied in many other research fields．But it is difficult to compute abductiVe expla-nations．In this paper，a method used in circumscription is given. When a theory is suited with complete axiom and positive reason assumption，it can be proved that the consistent exDlanation is exactly the abductive explanation in the circumscription. Furthermore, an algorithm using in Horn clauses is given．