Abstract: Displacement ventilation has been considered a good function of ventilation since it can provide good indoor air quality (IAQ) and save energy.Recently it has also been used in commercial buildings.However, if the floor of the room is not clean enough and is covered with some dust, the fresh air sent from the floor level will make the dust airborne and influence indoor air quality.This paper is to study the influence of dust on floor on the IAQ of displacement ventilated room.Because it was difficult to measure the initial dust quantity and particle size,experimentally,the computational fluid dynamics (CFD) method was used in this work.The Euler-Lagrange method was used to simulate this case.The dust concentrations at different supply air velocities and different particle sizes were stuied and the deposition of dust was compared as well.The result indicated that the quantity and particle size of dust on floor should be considered when choosing the mode of ventilation.