In studies of paleoclimate and paleoenvironment based on loess-palaeosol deposits, the rigorous relations between climate elements and the properties of loessic sediment are scarce because the dynamic processes controlled by the related physical laws are often ignored or arbitrarily simplified. In the current study, the horizontal distance of a suspended dust particle is re-estimated using classical mechanics and the relation between wind speed and the grain size of primary loess is then established. The actual application of this new theoretical relation is given by an example of Duowa profile, western Chinese Loess Plateau. The numerical results imply that the Qaidam Basin could be a likely dust source of the Chinese Loess Plateau.