This paper firstly proposed the definition of reasoning cycle, secondly gave some examples, thirdly analyzed and proved the causes of reasoning cycle. Based on above work, this paper proposed an algorithm for the elimination of reasoning cycle. This algorithm's thinking is to prevent sub-target from being isomorphic with its ancestral-targets. Comparing with other related work (for example, the reasoning tool PROLOG), this algorithm not only solved the problem of reasoning cycle which has not yet been solved by PROLOG but also processed patterns in the form of natural language instead of formal patterns. This algorithm's correctness is proved in theory and the experiment results indicate that this algorithm is correct.