Aim To find out the risk factors of in-hospital mortality in patients with acute ST-segment elevation myocardial infarction （STEMI） treated with primary percutaneous coronary intervention （PCI） and intra-aortic balloon pumping （IABP）.Methods We retrospectively studied 91 patients with STEMI who had undergone primary PCI and IABP in Nanjing Drum Tower Hospital from January 2010 to September 2014. Clinical and angiographic characteristics between the death group and the survival group were compared to fingure out the risk factors of in-hospital mortality.Results The patients in death group were older and had higher Killips classification at admission than those in survival group. No significant differences were found in other baseline clinical characteristics between the two groups. The total ischemic time and the frequency of IABP inserted before PCI were also similar in the two groups. TIMI 3 flow after primary PCI was positive predictor of the in-hospital mortality （OR＝0.462,P<0.05） while age （OR＝1.081,P< 0.05）,Killips class≥3 （OR＝6.703,P<0.01）,diseased left main trunk （OR＝7.273,P<0.05） and peak serum CK-MB concentration （OR＝1.003,P<0.01） were negative predictors of the in-hospital mortality.Conclusions For patients with acute STEMI treated with primary PCI and IABP,TIMI 3 flow after PCI can decrease the in-hospital mortality while older,Killips class≥3,diseased left main trunk and higher peak serum CK-MB concentrations can increase the in-hospital mortality.