Abstract: With the rapid development of major cities,Subway line has become an important traffic transportation in major cities.A subway line is an important and densely populated lifeline infrastructure.It is difficult to renovate it if a subway line is damaged during earthquake.Therefore,it has become more and more important in ensuring subway safety during earthquake.In this paper,based on the fifth subway line in Beijing,the relationships of ground motion parameters and response spectrums in different site conditions,different risk levels and different depths are discussed.It is determined that the 50 year exceedance probability 63%、10%、2% can be used as the subway earthquake fortification levels.The surface ground motion parameter can be used as the design ground motion parameter.Through studying seismic microzoning and response spectrum characters,this paper defined the earthquake fortification level for the fifth subway line.