Sand-blocking and sand-fixing belts, located in desert-oasis ecotones, are vital ecological barriers for maintaining oasis stability and mitigating wind-blown sand hazards in arid regions. The existing belts consist of a shrub zone and tree shelterbelt at the oasis margins. In this study, we focused on the Hexi Corridor and conducted simultaneous field measurements of near-surface wind speed and sand flow along five representative transects across these belts. Based on these observations, we developed a predictive equation for sand transport within the belts. We found that the reduction in near-surface wind speed within the shrub zone and oasis interior primarily depended on the lateral cover of shrubs and structure of the shelterbelt. The shrub zone was dominated by aeolian deposition, with significant variations in sand transport among transects caused by differences in belt structure and integrity, leading to variable sand-blocking and sand-fixing efficiencies. When the shrub zone failed to weaken the aeolian activity, the overall protective efficiency dropped below 40%, resulting in sand deposition along the edges of the shelterbelts between the shrub zone and the oasis farmland. The accumulation advanced by nearly 1 m toward the oasis, posing a direct threat to its ecological security. Controlling mobile dunes, restoring shrub zones, and optimizing shelterbelt structures are essential for enhancing the functionality of sand-blocking and sand-fixing belts. (c) 2025 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).