The paper analyzes the grain-size distribution of riverbed alluvial deposits in Harbin, and on that basis, combined with the grain-size distribution of sand-dust fallouts, it discusses the impact of bare riverbed alluvial deposits on the sand-dust weather. The analytic results show the following:the >63μm particles of bare riverbed alluvial deposits constitute >84% of the components, while the <63 μm particles are rare and those <10μm are very rare; the content of silt-clay particles <63μm amounts to >90%.