Abstract: The combination of water and sediment prompts the riverbed evolution. The movement forms, movement rules and the effects on riverbed having different sediment grain sizes are various. Thus, the studies of the riverbed evolution can not despise the sediment fraction and movement characteristics, particularly the studies of the Inner Mongolia reach of the Yellow River, of which water and sediment come from different areas. On the basis of the observed data from the hydrometric stations and by drilling samples, this paper shows the sediment fraction of the suspended material and bed load. Based upon these, the movement forms and rules of the main sediment fraction under certain hydrodynamic conditions are discussed, from the angles of starting velocities, suspended height and silt carrying capacity. The sediment transport rule of the bed load is found by an energy and power equation. The research results show that in the Inner Mongolia reach, the suspended material is mainly composed of the sediment whose grain size is less than 0.08 mm. And the primary partical size of the bed load is from 0.1 mm to 0.5 mm, especially the sediment with partical size between 0.1 mm and 0.25 mm is active during the erosion and deposition of riverbed. The analysis of the bed load transport rate indicates that the most of coarse particle silt, which comes from the upper reach of the Inner Mongolia reach, is too difficult to be carried downstream and will deposit on the riverbed of the upstream of Sanhuhekou.