Objective: To assess the value of different grading criteria of sacroiliac joint (SIJ) computed tomogrphy (CT) in ankylosing spondylitis (AS). Methods: Patients who had received SIJ CT examinations from June 2012 to December 2015 were enrolled.The CT scans were read by one rheumatologist.The difference between patients with sacroiliitis or without sacroiliitis was compared.The 1984 revision of modified New York (mNY) criteria, the criteria established by Lee (Lee criteria) and the Innsbruck criteria were used to evaluate SIJs on CT in patients with sacroiliitis. Results: Totally 2 714 patients were enrolled in this study.Thereinto 509 patients including 324 male and 185 female were detected with SIJs abnormality.The proportions of SIJs graded 3 or 4 by these three criteria were 79.37%, 82.91% and 76.32%, respectively.The consistency of grading between mNY criteria and Lee criteria was good (k=0.767, P<0.01). The correlation between Innsbruck criteria and other two criteria were satisfactory (r=0.866 and 0.839, respectively). There were more SIJs graded 3 by Lee criteria (64.44%), comparing with mNY criteria (60.90%). Forty five SIJs graded 1-3 by mNY criteria were graded 0 by Lee criteria, indicating that the latter criteria may have a better specificity. When evaluating the severity of SIJs, Innsbruck criteria has a better discrimination capability and the proportions of SIJs graded Ⅱ (A) to Ⅳ (B) were 10.71%, 8.94%, 26.82%, 20.92%, 10.12%, respectively. Conclusions: Lee criteria has a better diagnostic specificity with a reduction of difficulty in assessing procedure, while Innsbruck criteria is a more detailed grading system with a possibility to reflect the development of sacroiliitis.