Jiangsu Computer Rank Examination is a examination mechanism formed by Education Department, which gains the attention of universities and students. First, based on data collected from previous students' exeamination, this paper uses Information Gain and ID3 algorithm to construct a decision tree. Then, this paper extracts the classification rules from the decision tree, and discovers these rules of the accuracy and coverage. Finally, this paper predicts the ability of students to pass the exam by these rules. Experiments indicate that the decision tree has accurate prediction, which can dig out the key factors affecting students to pass the grade examination and plays a crucial role in the course teaching.