Air purifier is a device which is used to remove the contaminants from air in an enclosed area. And this numerical simulation is carried out to analyze the performance of air purifier. The turbulent model of URANS(Unsteady Reynolds Average Navier-Stokes) method has been used. Particle size and simulation time have been considered as 1μm, 2.5μm, 10μm, 100μm and 540 seconds, respectively. The main objective of this research is to propose the effects of the particle size and fan on the dust transport characteristics and to validate the dust collection performance of air purifier with experimental data.