The early stages of rheumatoid arthritis of the sacroiliac joint and sacroiliac tuberculosis, as well as the stage of bony ankylosis of both, are difficult to distinguish on radiographs. Both rheumatoid arthritis and tuberculosis can have early destruction of the sacroiliac joint surface, which is manifested by irregularity and blurring of the joint surface, followed by narrowing of the joint cavity and even bony ankylosis of the joint. In the differential diagnosis, the following points are available for reference: 1, tuberculosis mostly invades the unilateral sacroiliac joint, while rheumatoid invades the sacroiliac joint on both sides mostly, but the degree of lesion may not be symmetrical. 2, sacroiliac joint tuberculosis from the development of sacral tuberculosis or iliac tuberculosis, so, although the sacrum and iliac bone can be invaded, often more significant destruction of a particular bone. In rheumatoid sacroiliac arthritis, the difference in the degree of involvement of the two bones is not obvious. 3, sacroiliac joint tuberculosis easy to form abscesses, iliac bone destruction is serious, abscesses more in the back or hip. If the sacrum is severely damaged, the abscess is mostly confined to the pelvic iliopsoas muscle area. When the lesion has significantly damaged both sacroiliac bones, abscesses may occur in the back, buttocks and pelvis at the same time. 4.Sacroiliac joint tuberculosis can coexist with other tuberculosis (lung, kidney ……) coexist, while rheumatoid can coexist with other joint rheumatoid (spine, extremity joints). In addition to these two diseases, there are similar manifestations of sacroiliac joint brucellosis, when attention should be paid to the area of residence, occupation, laboratory tests and other symptoms.