Abstract: OBJECTIVE To investigate the relationship between CD64 index and secondary infection and disease activity in patients with systemic lupus erythematosus(SLE), so as to provide reference for the clinical treatment of secondary infection in SLE. METHODS A total of 92 cases of patients with SLE who treated in our hospital from Feb. 2014 to Feb. 2015 were selected and divided into bacterial infection group 46 cases and non bacterial infection group 46 cases, according to the laboratory results, and non bacterial infection group according to the activity index (DAL) were divided into active stage 24 cases and non active stage 22 cases, and 30 cases of healthy people were selected as control group. The average fluorescence intensity of CD64 on the surface of lymphocytes(L), granulocyte(N)and mononuclear cells(M) were detected by flow cytometry, and the CD64 index was calculated to analyzed the correlation between CD64 index and SLE infection index and disease activity index in patients. RESULTS The CD64 index in the bacterial infection group were significantly higher than the non bacterial infection group and control group (P<0.05).The levels of N, WBC, ESR, CRP and PCT in bacterial infection group were significantly lower than those in the control group and the non bacterial infection group (P<0.05). The bacterial infection group CD64 index and N,WBC,ESR,CRP,PCT were positively related(r=0.492,r=0.541,r=0.612,r=0.678,r=0.732,P<0.05) after the Pearson correlation analysis, but had no significant correlation to Ana, DS DNA antibody, complement C3 and C4. CONCLUSION The CD64 index of SLE patients with secondary infection is closely related to the infection and disease. In the clinical diagnosis,CD64 index can be used as the identification index of SLE secondary infection and disease activity.