To study the defining and quantification of the performance level of large span space structure under seismic motion, based on the singlelayer kiewitt reticulated dome, this paper defines the graded performance level. And then the structural damage model based on the multiple dynamic responses using the whole course analysis method was conducted. The different damage degree, the boundary value of graded performance level and the corresponding dynamic responses were quantified by this damage model. At last, the vulnerability analysis of the graded performance level of large span space structure was completed.