Abstract: Once gas flows into wellbore during drilling,two-phase gas-liquid flow will come into being.If it can not been controlled well,well blowout accidents are very likely to happen.In this paper,the flow pattern of two-phase gas-liquid flow in vertical annulus is analyzed using air-drilling fluid as medium to analyze the law of two-phase gas-liquid flow during gas kick,control gas kick and prevent well blowout.What's more,physical flow model for flow field is established.Simulation calculation is conduced on turbulent flow field using standard model,which shows that the law of two-phase gas-liquid flow before or after gas kick conforms to the actual flow of borehole fluid during gas kick.Furthermore,the flow pattern transition,the gas migration velocity,and the distribution law of annulus gas after gas kick are presented.Calculation results can be good reference to computer simulation of well control.