[Objective] The fractal dimension of particle size distribution in a basin with coupled wind-water erosion processes was studied to provide theoretical and experimental basis for the research and control of coupled wind-water erosion and hyper-concentrated flow sediment. [Methods] Xiliugou catchment, which is located in the upper stream of the Yellow River in Inner Mongolia Autonomous Region, was selected as the study area. Total 43 Surface sediment samples at different locations were collected in the catchment. The sediment grain size composition was measured by a laser particle size analyzer. Based on the fractal theory and using the ANVOA and K-means cluster methods, the fractal dimensions of particle size distribution in the Xiliugou catchment were obtained and its influencing factors were analyzed. [Results] (1) The fractal dimension of particle size distribution varied under different depositional environment. The highest fractal dimension(2.48) was found in the hilly-gullies region where water erosion prevail, and the lowest(1.87) in the desert region, where wind erosion is much active. (2) The fractal dimension increased with the increase of particles content lower than 0.05 mm, but decreased with the increase of particles content within 0.05~1 mm. The relation between the fractal dimension and the content of particles larger than 1 mm was not significant. The influence of silt content on the fractal dimension was greater than that of clay content. [Conclusion] The sediments on river bed in different geomorphic units had significant discrepant particle size composition and the particle size composition of sediments on berms changed evidently both in different geomorphic units along the river and in different depositional environment within the floodplains. The particle size composition of sediment sources, the regolith or loess, did not show obviously variations between different geomorphic units.