OBJECTIVE： To investigate the correlation of plasma concentrations of clopidogrel with coagulation function. METHODS： 126 acute coronary syndrome （ACS） patients underwent PCI were selected from our hospital during Jun. 2014-Jun. 2015. They were given maintenance dose （clopidogrel hydrogen sulfate 75 mg+aspirin 100 mg） before operation， qd， for consecutive 5 d； given loading dose （clopidogrel hydrogen sulfate 300 mg+aspirin 100 mg） at a draught one day before operation； given maintenance dose again after operation. On the second day of giving maintenance dose after operation， plasma concentration of clopidogrel was determined by LC-MS/MS； thrombelastography （TEG） was used to determine blood clot formation time [the formation time of first piece fibrae sanguis （R）+the time of blood clot strength reaching 20 mm （K）]， fibrae sanguis and blood clot consolidation time （expressed by Angle） and fibrae sanguis and blood clot final strength （MA）. Pearson test was adopted for relationship analysis. RESULTS： Average plasma concentration of clopidogrel was （82.3±20.1） ng/L， （R+K） was （7.8±2.4） min， Angle was （64.1±8.7）° and MA was （60.7±7.2） mm. Plasma concentration of clopidogrel was positively correlated with （R+K） （r＝0.671， P＜0.01） and negatively correlated with Angle （r＝－0.556， P＜0.01）. There was no correlation between plasma concentration of clopidogrel and MA （r＝－0.073，P＞0.05）. CONCLUSIONS： As plasma concentration of clopidogrel increased， blood clot formation time prolonged while fibrae sanguis and blood clot consolidation speed decreased.