Abstract: Based on the reactor building of a 1 000 MW Pressurized Water Reactor（PWR） nuclear power station, the floor response spectra in the use of power spectrum density functions has been generated, the main factors（such as soil-structure interaction, second-primary structure interaction and damping ration of secondary system） which have great effect on FRS is investigated with the base-isolation devices added in reactor building, and the sensitivity of the floor acceleration response spectra of the reactor building to the change of this main factors is quantitatively analyzed. The result show that the peak acceleration of FRS is effectively decreased with additional base-isolation devices, and it mainly appears near the base-isolation frequency;in the same time, the base-isolation effect, SSI and second-primary structure interaction are with cross effect, and it is necessary to consider all the effects in the design of nuclear reactor buildings.