Abstract: Background Understanding the development of soil preferential flow and its influencing factors under different sand-fixing vegetation on dune slopes in the Mu Us Sandy Land is of great practical significance for regional vegetation restoration and rational water resource utilization. This study quantitatively examined the effects of typical vegetation types on the spatial patterns of preferential flow, aiming to provide theoretical support for maintaining the stability and sustainable management of arid sandy land ecosystems. Methods This study selected dune slopes covered by different vegetation types—Juniperus sabina, Pinus sylvestris var. mongolica, Artemisia ordosica, and Salix psammophila—within the Hailiutu River Basin, with bare mobile dune slopes as a reference. Field dye-tracing experiments were conducted at three infiltration levels (15mm, 30mm, and 50 mm). Image processing techniques were applied to extract staining morphology parameters, and these were combined with measurements of soil physicochemical properties and root characteristics to systematically analyze the development characteristics of preferential flow on slopes under different infiltration amounts. Results 1) The preferential flow evaluation index(PFI) ranked as follows: Pinus sylvestris var. Mongolic > Juniperus sabina > Artemisia ordosica > Salix psammophila > mobile dune. The preferential infiltration proportions in Pinus sylvestris var. mongolica and Juniperus sabina plots reached 57.95% and 50.71%, respectively, significantly higher than those in other vegetation plots and the mobile dune (P < 0.05). 2) A significant positive correlation was observed between the root length density of roots with a diameter ≥ 2 mm and the PFI (r = 0.46,P < 0.05), indicating that coarse roots are a key factor regulating preferential flow formation. 3) As the infiltration amount increased, the preferential flow ratio on dune slopes showed a decreasing trend. Under high infiltration amounts, soil water movement in sandy soil tended to become more uniform. Conclusions This study demonstrated that vegetation type significantly influenced preferential flow development on sand dune slopes, with Pinus sylvestris var. mongolica and Juniperus sabina promoting the most pronounced preferential flow. Coarse roots (≥2 mm) played a critical role in creating and stabilizing preferential flow pathways. Furthermore, the infiltration amount modulated preferential flow expression, with higher inputs leading to more uniform wetting. These results provided a scientific basis for optimizing vegetation configuration—considering species-specific impacts on soil water redistribution—and improving soil moisture management practices in the Mu Us Sandy Land, ultimately supporting more effective ecological restoration and water conservation strategies.