The previous research shows that ITR has more merits than CTT in the evaluation of examination. Based on the data collected in math subject in National College Entrance Examination of one district, the paper compares the differences between CTT and IRT on project parameters, ways of evaluation and accuracy assessment. The research shows that the characteristics of each project properties are more easily reflected under the IRT parameters, and the IRT parameters are more accurate than the CTT. The function of the project information can reflect the information of the tests better. IRT and CTT have different evaluation ways and the scores under the evaluation of IRT, which represents students' abilities, are higher than those of CTT. CTT is different from IRT in precision estimation, but the test information function and confidence interval of IRT are more accurate than that of CTT. The Empirical study shows the advantages of IRT in evaluating the math subject in College Entrance Examination, which is valuable and has potential applications.