Research status of ground motion parameters of seismic appraisal for existing structures is analyzed. According to the theory of the probabilistic distribution of seismic intensity which fits Extreme Value Type Ш, the relation of multi-value seismic intensity to seismic basic intensity from different seismic hazard characteristic zone is studied in this paper. Under the principle of all the seismic actions of each fortification level have the same exceeding probability, the basic intensity for seismic assessment of buildings with different residual service lives is given to each zone. At last, after giving full consideration to the seismic hazard differences to different areas, the modification factors of seismic action of buildings at the three zones with different seismic hazard characters are given in this paper. At last, this paper provides a base for the structure designers to choose a rational seismic action during the seismic appraisal for existing structures.