Abstract: A nonlinear random dynamic mode with stochastic variations of seismic action and structural parameters is constructed. The incremental formulae of dynamic analysis on nonlinear stochastic finite element method are also given, which hare been used for the seismic response analysis of reinforced concrete multistory buildings at elastoplastic stage. The calculated results are in good agreement and those of the actual damaged buildings in earthquakes. In addition the effects of the stochastic variations of structural parameters and seismic action in random dynamics model on the seismic response of the structure are investigated in detail.