Objective To investigate the percentage of CD4+CD25+ Treg in peripheral blood of patients with severe multiple trauma and systemic inflammatory response syndrome（SIRS） and its effects on cellular immunity and secondary infection.Metheds Peripheral blood of 23 patients with severe multiple trauma was collected in 24 h after SIRS was diagnosed，and flow cytometry was used to determine the percentage of CD4+CD25+ Treg and CD4/CD8 ratio.Simultaneously，in order to explore the cell proliferation，silver staining was used to determine Ag-NORs of leukomonocyte in peripheral blood represented by IS%.In order to investigate the infection in patients，sputum and secretion sample were collected for bacteriological examination on 1 and 5 day after SIRS was established.Forty healthy volunteers were enrolled as control.Results Compared with the control，the percentage of CD4+CD25+ Treg was significant higher[（14.21±3.43）% vs（9.53±3.22），Plt;0.01] and the ratio of CD4/CD8 and IS% were significant lower in patients with severe multiple trauma[（5.94±0.66）% vs（6.74±0.95）%，（1.22±0.25）% vs（1.72±0.36）%，respectively，both Plt;0.01].In those patients（n=14） who developed secondary infection，Treg% was significant higher [（18.69±4.21）% vs（12.58±2.49）%，Plt;0.01]，while IS% and CD4/CD8 were significant lower [（5.79±0.68）% vs（6.15±0.57）%，（1.15±0.25）% vs（1.39±0.25）%，both Plt;0.01].compared to the patients without secondary infection Conlusion CD4+CD25+ Treg is valuable to estimate the cellular immunity and predict secondary infection in patients with severe multiple trauma.