Objective To investigate the relationship between suspected ankylosing spondylitis and HLA‐B27 antigen by detec‐ting the positive frequency of HLA‐B27antigen in 872 suspected AS patients ,and evaluate its clinical significance .Methods The positive frequency of HLA‐B27 on the T lymphocyte membrane were detected by flow eytometer in 872 suspected AS patients .Re‐sults Among the 872 suspected AS patients the ratio between male and female was 1 .8∶1 ,the positive rate of antigen HLA‐B27 was 27 .29% ,and the male and female patients′positive rates of HLA‐B27 antigen were 32 .50% and 17 .95% ,respectively (P<0 .05) .The male and female patients′ expression percentage of B27+ /B7- monoclonal antibody were 39 .16 ± 42 .79 and 20 .96 ± 33 .86 ,respectively(P<0 .05) .The male and female patients′mean fluorescence intension of B27+ /B7- monoclonal antibody were 5 .35 ± 5 .44 and 3 .35 ± 3 .87 ,respectively(P<0 .05) .Conclusion The patients with AS are strongly associated with HLA‐B27 an‐tigen .Detection of HLA‐B27 antigen expression intensity in suspected AS patients with FCM is helpful to diagnosis and differential diagnosis of AS .