Abstract: Sediment gyration sampling was conducted in June 2006 to analyze the profile distribution of sediment particle sizes at a check-dam built in 1954 in
a typical small watershed of hilly and gully Loess plateau. There were at least 28 layers of sediment gyration at the check-dam, with the layer depth varied from 2 cm to 60 cm. In the sediment profile, silt (0.05-0.002 mm) occupied >60%, its particle size being mainly within the range of 0.01-0.05 mm, while coarse sand (>0.05 mm) accounted for 23.09%. The variation degree of sediment particle sizes increased with increasing depth, an
d an abrupt change was observed at the depth 2 m. Both longitudinal gradient and hydrodynamic condition caused the variation of sediment particle sizes. There was an accumulated plough layer of 72 cm thickness in the profile, which had indicative role for the sediment erosion environment of check dam.

Key words: Loess Plateau, check dam, sediment particle size, gyration, erosion process, maize, hybrid, shade-humid environment, index.