To explore clinical efficacy of modified Chaiqin Chengqi Decoction combined with western medicine in severe acute pancreatitis，and to study its mechanism of action in order to enrich treatment methods，reduce complications of severe acute pancreatitis and improve the efficacy.Methods:A total of 62 patients with severe acute pancreatitis admitted to Mianyang Central Hospital from January 2017 to February 2018 were selected as subjects.They were numbered in order of treatment and divided into control group(31 cases)and observation group(31 cases)according to random number table method.The control group was given ECG monitoring，fasting，fasting water，gastrointestinal decompression，acid suppression，maintaining internal environment stability，antimicrobial，inhibiting pancreatic secretion and pancreatic activity，analgesia and other treatments.The observation group was given modified Chaiqin Chengqi Decoction on the treatment basis of the control group，and was given the medicine through gastric tube.They were treated for 2 weeks.Changes of serum amylase and lipase were observed and compared before and at the end of the treatment; and changes of WBC，CRP，endotoxin and IL-6 were observed and compared before and at the end of the treatment; indexes of immune function like CD4+，CD8+ and CD4+/CD8+ were observed and compared before and at the end of the treatment; adverse reactions during the treatment were observed and compared; and the efficacy at the end of the treatment was compared.Results:1)There was no significant difference in the blood amylase，urine amylase and lipase between the 2 groups before the treatment(P>0.05).At the end of the treatment，the above indexes in the 2 groups were significantly lower than those before the treatment(P<0.05).At the end of the treatment，the above indexes in the observation group were significantly lower than those in the control group(P<0.05).2)There was no significant difference in the WBC，CRP，endotoxin and IL-6 between the 2 groups before the treatment(P>0.05).At the end of the treatment，the above indexes in the 2 groups were significantly lower than those before the treatment(P<0.05).At the end of the treatment，the above indexes in the observation group were significantly lower than those in the control group(P<0.05).3)There was no significant difference in the CD4+，CD8+ and CD4+/CD8+ between the 2 groups before the treatment(P>0.05).At the end of the treatment，the CD4+ and CD4+/CD8+ in the 2 groups were significantly increased compared with those before the treatment，while the CD8+ was significantly decreased(P<0.05).At the end of the treatment，the above indexes in the observation group were significantly better than those in the control group(P<0.05).4)After the treatment，the cure rate and total effective rate in the observation group were significantly higher than those in the control group(P<0.05).5)There was no significant difference in the incidence of nausea，vomiting，abdominal pain，diarrhea and dizziness between the 2 groups(P>0.05).Conclusion:Chaiqin Chengqi Decoction can inhibit serum amylase and lipase，inhibit inflammation response，improve immunity and improve efficacy in severe acute pancreatitis.