Abstract: Taking driving speed and merging angle as the characterization parameters of merging traffic conflict,the conflict time as the measurement index of merging conflict risk was proposed and the calculation model on merging conflict risk was established based on analyzing the characteristic of merging behaviour at freeway work zone. The merging conflict risk threshold value of freeway work zone was defined under different safety instances. The GM(1,1) prediction model on merging conflict was developed based on grey theory. And the prediction model was validated using merging conflict sample data. Research results show that the risk threshold value of merging conflict of freeway work zone is dangerous,moderate and security,which is(∞,5) km/h,(3.55,5 km/h and(0,3.55 km/h respectively under different security state,and merging conflict prediction model of freeway work zone based on GM(1,1) is efficient and reliable,which can meet the accuracy requirement.