Before the 1970s, ankylosing spondylitis was the central form of rheumatoid arthritis. So that after the 1970s, it was thought that this disease was not a class of disease at all, so ankylosing spondylitis was separated from rheumatoid arthritis. The specific differences are as follows: 1, rheumatoid arthritis, female onset more than male, ankylosing spondylitis is exactly the opposite; 2, rheumatoid arthritis can occur in all age groups, with a peak age of 30-50 years, ankylosing spondylitis occurs in young people, with a peak age of 20-30 years; 3, most patients with ankylosing spondylitis are HLA-B27 positive, while rheumatoid arthritis is mainly rheumatoid factor CCP antibody positive; 4, rheumatoid arthritis is mainly in the small joints of the extremities, more in the upper extremities than in the lower extremities, while ankylosing spondylitis is mainly in the small peripheral joints, more invasive of the medial joints, more in the lower extremities than in the upper extremities, more large joints than small joints; sacroiliac arthritis is very rare in rheumatoid arthritis, but up to 90% in ankylosing spondylitis, some symptoms outside the joints of rheumatoid arthritis, with subcutaneous nodules, iritis In rheumatoid arthritis, some symptoms outside the joints, such as subcutaneous nodules, iritis, pleurisy are more common, while in ankylosing spondylitis, iridocyclitis and thrombophlebitis are more common; 5. X-ray manifestations of rheumatoid arthritis are more common with osteoporosis and bone erosion around the joints, and rarely with calcification and ossification, while in ankylosing spondylitis, calcification, ossification and bone erosion are more common.