River sediments respond sensitively to the basin environmental changes and particle size parameters can reflect the material sources and hydrodynamic environment. This article takes the Heihe River as a case to explore the response of river sediment grain size to the basin environmental changes. River sediment samples were collected from 22 sections along the mainstream of the Heihe River. Then, sieving and pipette methods were applied to measure the particle size. Spatial variations of grain size parameters and their responses to the anthropogenic environmental changes of the basin through river damming were analyzed. The results showed that the grain size of the upper and middle reaches of Heihe River was significantly different under the influence of the construction of cascade reservoirs. The grain size of reservoir sediment decreased more obviously in the river section within cascade reservoirs than in the original natural reach, and the sediments are characterized by well-sorted, with acute kurtosis and positive skew or very positive skew. In addition, the sediment grain size shows the characteristics of layered sedimentary at different depositional heights in the reservoirs. The downstream river of the Dam was suffering from strong erosion, and the grain size of bed sediments is coarse and poorly sorted, and the grain size distributions are more positively skewed with sharp kurtosis. The backwater area of the reservoir is restricted by backwater and drainage water, and the sediment particle size is between the original natural river and the downstream river of the dam, with middle sorted sediments, positively skewed grain size distribution and acute kurtosis. Sedimentary environment analysis reveals that the sediments grain size characteristics of upstream tributary are more influenced by material sources than hydrodynamic conditions, while the grain size characteristics of main stream sediments are mainly controlled by hydrodynamic conditions. The results are consistent with the normal pattern of sediment grain sizes distribution in rivers, and also reflect the impact of environmental changes on river sediment grain size composition.