Item response theory provides a fixed results about students, regardless of the item difficulty and discrimina-tion and it is also a kind of item analysis methods which provides the same proper competence scores to students in spite of them taking different test repeatedly. In this paper, we researched item difficulty and item discrimina-tion and analyzed items in the national academic aptitude test which were given from 2000 to 2009 in the past 10 years through item response theory, especially, in connection with given items about statistical unit. As a result, we found that about 60 percents of the items were too difficult for high school students to solve, however, item discrimination proved to be great.