Objective: systemic lupus erythematosus (SLE) is easy to break out repeatedly, it is very importance to treatment that the assessment of disease activity. This paper studies neutrophils and lymphocytes ratio (NLR) and the ratio of neutrophils and C3 complement (NC3R), and the correlation of active SLE. Method: 189 subjects with SLE, 91 subjects with RA and 71 healthy people were included. To determine the laboratory indicators and compare the differences of NLR and NC3R among three groups. Then evaluated NLR, NC3R correlation with SLE activity. Result: The level of NC3R and NLR within the three groups were different(P＜0.01). SLEDAI scores positively correlated with NC3R (r=0.449, P＜0.01) and NLR (r=0.267, P＜0.01). Receiver operating characteristic (ROC) curve analysis showed that the cut-off value of NC3R to predict SLE with high disease activity was 5.85, with 52.9% sensitivity and 93.7% specificity, while that of NLR was 3.14, with 42.3% sensitivity and 87.3% specificity. Conclusion: NC3R and NLR may be used as an auxiliary indicator to assess the activity of SLE and guide the treatment.