Abstract： Objective To find the factors lowering the rate of effective thrombus aspiration in patients with STsegment elevation acute myocardial infarction (STEMI) treated with primary percutaneous coronary intervention(PCI). Method From January to December 2008 , a total of 226 AMI patients from Beijing Anzhen Hospital,treated with primary PCI to aspirate the thrombus from the infracted coronary artery via a cannula, were enrolled in a single center retrospective study. The criterion of successful thrombectomy (device success) was defined as the coronary blood flow of involved vessel after PCI resumed to greater than TIMI grade 1. One hundred seventy-eight patients were assigned to effective thrombus aspiration group, and 48 patients without improvement in coronary blood flow of involved vessel after PCI to control group. Data collected after PCI including the normalization of the elevated ST segment,the use of direct stent, ratio of no-flow/slow flow, intra-coronary administration of Tirofiban and the rate of thrombolysis in myocardial infarction (TIMI) flow grade 3 were analyzed with logistic analysis soas to find out the factors affecting the efficacy of thrombus aspiration. Results There were no significant differences in data before PCI between two groups ( P ＞0.05). Compared with the control group, the factors studied such as smoke, diabetes, the rate of pre-PCI TIMI flow grade 0,the post-PCI ratio of no-reflow/slow flow,and the intra-coronary administration of Tirofiban were fewer significantly in the effective thrombus aspiration group. And the rate of post-PCI TIMI flow grade 3, and the rate of direct stent were higher in the effective thrombus aspiration group. Logistic analysis showed that smoke ( OR = 1.551,95%CI: 1.018 ～ 2. 154, P = 0.012), diabetes ( OR = 1. 132,95%CI:0.276 ～ 3.562, P =0.044), and pre-PCI TIMI flow grade 0 OR = 0.544,95%CI:0.368 ～ 1.911,P = 0.035) were independent factors of effective thrombus aspiration. Conclusions Effective thrombus aspiration may improved the coronary blood flow to TIMI flow grade 3 after PCI and reduce the impaiment of myocardial perfusion, and the factors affecting the efficacy of thrombus aspiration should be paid more attention to and should be minimized to achieve the better clinical outcomes.