This paper analyzes the characteristics of the gray literatures and discovers the existing problems of the quality control to the gray literatures in the university institutional repository. Based on the deficiency, this paper proposes an effective method for solving these problems. The essence of the method is to construct an evaluation index system and a users' credibility evaluation index system. And through the weights of the both indexes, we can obtain the evaluation weight for the gray literatures. Then giving different literatures with different access rights according to the evaluation weight with grouping criteria based on what we classify the literatures. By using this method can we construct quality control mechanism of gray literature for university institutional repository and root up the problems above-mentioned.