Background, aim, and scope Sediments from shallow salt lakes in arid basins are important carriers for reconstructing the past global climatic changes. The grain size of sediments in such lakes provides basic understanding of the lake hydrodynamics, geomorphology and sedimentology. However, as a simple physical indicator, the grain size could be differently interpreted in different lakes. Here we present a detailed study on the relationship between the grain size of surface sediments and hydrological conditions including water level and hydrodynamic changes within Xiao Qaidam Lake, a shallow salt lake in Qaidam Basin, NE Tibetan Plateau. Materials and methods Surface sediments (23 samples) were collected along two sampling routes across the lake from south to north of the lake. Two aeolian sand samples around the lake and one short core (XCD3, 93 cm) sediments were used for comparisons. The grain size frequency curves, average grain size, sorting, skewness and kurtosis were calculated based on the measurements of Malvern MS 2000. Results Results suggest that the grain size of the sediments becomes finer with the increase of water depth. The average grain size of the surface sediments is 5.3-31.8 mum. The sorting coefficient ranges from 1.36 to 2.59 and the kurtosis varies between 0.69 and 1.18, with skewness between -0.25 and 0.37. In deeper water area (>200 cm), the median grain size is less than 11.2 mum and the frequency curves show a similar unimodal distribution. In the shallower water (<200 cm), the median grain size is much coarser and the frequency curves show different multi-peak distributions, resulting from the combination of processes. Discussion According to the data of maximum wind speed from 1956 to 2013 at the Qaidam weather station, the maximum depth influenced by wind-waves is calculated to be 40 cm, indicating the surface sediments under water depth >40 cm cannot be affected by the wind-waves. Similar grain size characteristics are found between core and surface sediments. Two stages in the short core (68-70 cm and 77-80 cm) show a similar grain size characteristic with aeolian sand around lake, indicating rapid drop of the lake level and aeolian sand reached the core site. The remaining stages demonstrate a relatively stable lake level, which is close to that of the modern. Conclusions (1) There is a decreasing trend in lake sediment grain size with the increasing of lake depth and the distance from the shore to the center of the lake. (2) The samples' grain size frequency distribution curves have a good consistency at the case of the lake water depth beyond 200 cm, indicating that the sedimentary environment of the Xiao Qaidam Lake is relatively stable in deep water with small external forces. (3) The characteristics of sediment grain size in the shallow lake area are complex, which is significantly affected not only by hydrological settings but also surrounding landform and vegetation in lake. Recommendations and perspectives Therefore, the characteristics of grain size in sediments from shallow lakes are complex, significantly affected not only by hydrological settings but also surrounding landform and vegetation. Detailed investigations on surface sediments are necessary before grain size of core sediments could be used for paleoenvironmental reconstructions.