Abstract： Objective To evaluate the efficacy and safety of intra-aortic balloon pump (IABP)counter pulsation in the treatment of ST-segment elevation myocardial infarction (STEMI) with concurrent left main coronary artery (LMCA) disease.Methods A retrospective analysis was performed on 305 patients with confirmed STEMI due to LMCA occlusion ( ≥ 50％ ) by coronary angiography.They were divided into IABP and non-IABP groups according to the application of IABP or not.Two groups were further divided into 2 subgroups according to the treatment with percutaneous coronary intervention (PCI) or drug alone.Short and long-term clinical efficacies and the incidence of complications caused by the application of IABP were analyzed in all groups and subgroups.Results ( 1 ) PCI procedure:Successful rate of immediate post-procedure was 100％.No death,major cardiovascular event and cerebrovascular accident occurred during the procedure.The average number of stents per patient was 2.1 ± 0.7 and the average diameter and length of stent were(3.9 ±0.6)and (24.2 ±7.1 ) mm respectively.(2) Safety:No significant difference existed between the IABP and non-IABP groups in in-hospital massive bleeding rate (0.94％ vs 1.00％,P ＞0.05).However,the IABP group had a higher prevalence of mild in-hospital bleeding than the non-IABP group.(3) In-hospital and long-term major adverse cardiac event (MACE) rate:① IABP group had a lower MACE rate (25.3 ％ (24/95) vs 38.5％ (57/148),P ＜ 0.05 ).②In spite of IABP implantation,the PCI subgroup had significantly a lower mortality rate than the drug subgroup (7.2％ (6/83) vs 25.0％ (6/24),P ＜ 0.05 ).③The combined use of PCI and IABP was superior to other regimens with regards to decreasing short and long-term mortality ( 11.2 ％ ( 12/ 107 ) and 25.3 ％ (50/198),P ＜ 0.01 ).Conclusion PCI is feasible and safe for the STEMI patients with LMCA and better short and long-term efficacies may be achieved.The use of IABP in the treatment of LMCA-related STEMI reduces MACE rate and improves survival rate.