Through comparing the algorithm of Peking University with the traditional algorithm, this paper builds a Representative Student Model and analyzes the utility difference of different types of students under this two kinds of algorithm; and through simulating the distribution of total students' grade, this paper also examines the differentiation of school's welfare resulted from different kind of algorithm of GPA. The result of this paper shows that the algorithm of Peking University is more useful for promoting fairness, as well as more useful for improving the entire welfare of students.