Abstract: A suit of ground motion fields was established by simulation；with a simple structure subjected to multiple support excitations，and by using incremental dynamic analysis and statistic inference method，the applicability of response spectrum acceleration of the interesting part of the structure as intensity measure of ground motion field was studied，the probabilistic distribution of structural engineering demand parameters at given intensity measure level was studied and the seismic performance of the structure at a given seismic hazard level was estimated. The study shows that response spectrum can be regarded as the intensity measurement of a multiple-support excitation and can be used to perform probability-based structural seismic performance estimations.