Abstract: Objective　To observe the anatomical characteristics in the CT appearance of normal sacroiliac joint (SIJ) space in different age groups, and to provide basis for diagnosis of SIJ subluxation.　Methods　The statistical analysis of CT images of normal SIJ space was performed in 480 patients.  The differences of SIJ space width in different ages, genders, levels and regions were compared.　Results　(1) There were significant differences in the widths of SIJ space in different age groups. With the increasing of age, the width of SIJ space decreased gradually. (2) The width of SIJ space in women was slightly greater than that in men, and there was no significant difference between them. (3) There were significant differences in the widths of SIJ space in different transverse levels. The lower part of SIJ had the minimum space width. (4) There were significant differences in the widths of SIJ space in the ipsilateral anterior, middle and posterior regions, while there was no significant difference between the left and right side of the same region.　Conclusions　The width of SIJ space is age-related, spatial  heterogeneity and diversity. This study provides reference for imaging anatomy of sacroiliac joint space width in different age groups. 

Key words: Age, 　Genders, 　Sacroiliac joint space, 　Imaging anatomy, 　CT