The competence of resisting nature extreme disaster is widely concerned after Fukushima nuclear incident in Japan. Many countries carry through investigation actively. The seismic is one of primary threatens for nuclear power plant safety. Therefore the seismic ability of nuclear power plants becomes the investigative emphasis. The floor response spectra is the input of the seismic design for nuclear plant systems, structures and components,and the important part of the seismic design, which is holding the balance in nuclear plant seismic safety. In this paper we use the third generation nuclear power plant example that is ACP1000 normal design excogitated by the China Nuclear Power Engineering Co., LTD. themselves to expatiate the reasonable seismic input and the advanced analysis method for China. Through introducing the input, the analysis process and the method about the ACP1000 floor response spectra are calculated. Then it has significant effect for improving the nuclear power plant seismic design and seismic safety.