This study presents a simplified model for vibration assessment of floors under walking load. The model is developed by converting the floor system into an equivalent SDOF model using transformation factors and applying simplified forcing functions to simulate the walking. The accuracy of the proposed model is verified against experimental tests and detailed FE analyses. A parametric study is also carried out on 67 floors with a wide range of design parameters. The results show that, unlike most existing simplified vibration analysis methods which have a limited application range, the proposed model is able to accurately capture the peak acceleration of floors with different frequencies and structural systems. The model is used for the vibration design of modular hospital floors. It is demonstrated that the proposed SDOF model greatly facilitates the design of modular floors with high natural frequencies, which is impractical to do with existing simplified vibration analysis methods.