This paper proposes a new n-gram matching approach for retrieving the supporting evidence, which is a question related text passage in the given document, for answering Yes/No questions. It locates the desired passage according to the question text with an efficient and simple n-gram matching algorithm. In comparison with those previous approaches, this model is more efficient and easy to implement. The proposed approach was tested on a task of answering Yes/No questions of Taiwan elementary school Social Studies lessons. Experimental results showed that the performance of our proposed approach is 5% higher than the well-known Apache Lucene search engine.