Objective：To explore the application of injury severity score（ISS） and new injury severity score（NISS） for assessing the treatment outcomes in blunt trauma patients，and to define the severe injury with ISS and NISS. Methods：Ａbbreviated injury scale （AIS 2005） was used to carry out retrospective analysis among 2 694 blunt trauma patients（≥2 regions，dividing six body regions by ISS） treated at Chongqing Emergency Medical Center from November 2005 to November 2011. In the meantime，the severe in－jury with ISS and NISS were defined and their relations with mortality were analyzed by Chi-square test and t test，logistic regression analysis and ROC. Results：The mortality rate was 6.9%（16/231） when ISS was 21-25 points while that was 13.0%（21/162） when ISS was 26-30 points；the mortality rate was 5.3%（21/399） when NISS was 26-30 points while that was 11.9%（15/136） when NISS was 31-35 points；there was no significant difference between them and 10% mortality（P ＞0.05）. Both ISS and NISS had positive linear correlation with mortality（r=0.787，P<0.001；r=0.845，P<0.001）. Patients with ISS and NISS 0-20 points had lower risk than those with other points of ISS and NISS. With the increase of ISS and NISS points，the risk of death was on the rise. ISS was not superior to NISS in predication of mortality（P＞0.05）. The most Youden indexes were 17.5 and 23.0 for ISS and NISS，respectively. Conclusion：Both ISS and NISS work well in evaluation the treatment outcomes in blunt trauma patients. It is reasonable to definite the severe poly-trauma by ISS≥18 and NISS≥23 in AIS 2005.