Objective To explore the changes of renin-angiotensin-aldosterone system in pediatric severe sepsis treated with continuous blood purification(CBP).Methods Prospective study,35 cases of critically ill children diagnosed with severe sepsis and admitted to PICU of Shanghai Children's Hospital of Shanghai Jiaotong University from June 2012 to May 2014 served as reseach objective.Based on the monitoring of vital signs,including central venous pressure,arterial blood pressure,mean arterial pressure,patients were treated with conventional therapy,as antibiotics,fluid therapy,and CBP by mode of continuous veno-venous hemodiafiltration or high volume hemofiltration.Plasma levels of rennin activity,angiontensin Ⅱ and aldosterone were measured by radioimmunoassay before and 24 h after CBP.Twenty-five cases of blood samples taken from the children collected from health care for liver function examination were matched as control group.Results Plasmalevelsofrenninactivitywere(2.11 ±1.93) pg/(L·h),(1.27±1.56) μg/(L·h),(0.37 ± 0.22) μg/(L· h) before and 24 h after CBP and control group,respectively.The levels of angiontensin Ⅱ were (426.78 ±332.37) ng/L,(364.40 ± 325.51) ng/L,(41.70 ± 10.81) ng/L,respectively.And the levels of aldosterone were (255.12 ± 218.18) ng/L,(134.92 ± 104.13) ng/L,(106.88 ±43.18) ng/L,respectively.The plasma levels of rennin activity,angiontensin Ⅱ,and aldosterone were higher in sepsis cases than in control group,while decreased obviously after CBP treatment(P ＜0.01,P ＜0.05).Eleven cases died and mortality was 31.4％ (11/35).After 24 h of CBP,the mean arterial pressure improved in 26 cases with septic shock and dopamine dose reduced(P ＜ 0.01).Conclusion The reaction of renin-angiotensin-aldosterone system is increased significantly in pediatric severe sepsis.CBP can down-regulate the levels of rennin activity,angiotensin Ⅱand aldosterone,but not worsen the circulation function.