This paper presents a numerical analysis of the emission process of volatile organic compound(VOC) from building material and its diffusion in a room. A polypropylene styrene-butadiene rubber(SBR) floor plate is chosen as the emission source of VOC. This study investigates spatial concentration distributions and time history of room-averaged VOC concentration for both with and without flushing. The results of this study show that for calculation based on ten-days period the room averaged VOC concentrations with and without flushing are quite different. the results thus suggest the need of flushing for new buildings.