Abstract: To investigate the dynamic performance of large-span composite floors and the vibration reduction effect of porous polyurethane pad floating slabs, a 10-story comprehensive office building dance rehearsal hall was taken as the research object. On site measurements were conducted on the dynamic characteristics and acceleration response of large-span composite floors under rhythmic jumping excitation. The mechanical properties of the porous polyurethane pads were examined, and their vibration reduction mechanism was discussed. The results show that the vertical natural frequencies and mode shapes of the large-span composite floor slab obtained from environmental excitation, impact hammer testing, and ABAQUS finite element method analysis are generally consistent, with an average damping ratio of about 0.026. Rhythmic jumping causes significant acceleration responses in the large-span composite floor slab. The dynamic elastic modulus of porous polyurethane is about twice its static elastic modulus, and the damping ratio is approximately 0.06. The large-span composite floor with floating slab can be regarded as a two degree-of-freedom system, and the structural dynamic response can be effectively reduced by adjusting the stiffness of floating slab damping pads and the mass of floating slab. After installing floating slab, the vibration reduction rate of the large-span composite floor under rhythmic jump excitation can reach more than 40%, significantly improving the comfort for the building’s multifunctional use.