Objective To investigate the diagnostic value of multiplex polymerase chain reaction (m-PCR) for diagnosing second infection of severe acute pancreatitis ( SAP), and to provide evidence for anti-infection treatment of SAP .Methods From January 2011 to December 2014 , thirty five patients of SAP were enrolled .Seven to fourteen days after SAP onset , patients′blood samples were taken and the presence of infection was determined by mP-CR.In the meantime, peripheral blood or the paracentesis fluid was cultured , and the result of culture was regard as golden standard to diagnose infection .Rseults The m-PCR could simultaneously detect 9 kinds of intestinal resident pathogenic bacteria , and the lower limit of detection was 10~1 000 copies.The detection rates were as follows (cultivation vs. m-PCR):staphylococcus aureus 6 vs 5 cases, staphylococcus epidermidis 11 vs 9 cases, enterococcus faecalis 2 vs 3 cases, enterococcus faecium 6 vs 7 cases, escherichia coli 19 vs 17 cases, klebsiella pneumoniae 2 vs 3 cases, pseudomonas aeruginosa 6 vs 4 cases, acinetobacter baumannii 2 vs 2 cases, malt narrow food aeromonas 4 vs2 cases.The 7th~14th days after SAP onset, the blood or paracentesis fluid culture was positive in 27 patients,and negative in 8 cases. And the m-PCR results were positive in 30 patients, and negative in 8 cases.The m-PCR results were positive in 30 patients, negative in 5 patients.The m-PCR results were positive in 3 patients who had negative culture results.In the remaining 32 cases, the results were consistent between the two detection methods .When the culture result was regarded as golden standard , the sensitivity, specificity and accuracy of m-PCR were 100%, 62.5%and 91.43%, respectively.The positive predictive value and the negative predictive value were 90%and 100%, respectively.It took (26 ±15) hours on average to obtain the result of culture method , and it took (102 ±32) hours on average to obtain the confirmative results .It took (12 ±8) hours on average to obtain the result of the m-PCR method.The time course of m-PCRwas significantly shorter than that of the traditional culture method, and the difference was statistically significant (P<0.05).Conclusions The m-PCR method can be used to monitor the bacterial infection in patients with SAP .The m-PCR method is a highly sensitive and rapid detection approach , which is worth of clinical application .