Abstract: The trajectory function of a single aerosol particle in a dilute gas system close to a wall was theoretically studied with consideration of different forces such as gravity-buoyancy, particle-wall interaction and Brownian force. The results indicate that there is a wall effect layer in which the particle shows a different dynamic characteristic from that in unlimited space. The wall effect layer is about 50 radii of the particle, which is much higher than the effective range of particle-waU interaction, about 1 radius. Finally, associated discussion was made to understand the effects of surface characteristic and particle size on the wall effect layer.