The transport and deposition of urban dust are highly relevant to the composition of its grain diameters. Generally speaking, coarse grains, mediate to fine grains and extremely fine grains are transported in the forms of rolling, skipping, and suspending, respectively. Urban dust grains in Xi'an come primarily from particles transported by means of skipping through relatively long or great distance, next from those transported by means of rolling from a short distance away, and, to a lesser amount, from those carried in the form of suspending through a long distance, with the last form only accounting for approximately 12% of the total grains.