The transition zone from drought to wetness is affected by the interaction of wind and water. The interaction forms a wind-water composite landform which is significantly different from wind and water. Exploring the interaction of wind and water is helpful to understand the geomorphic process of arid-humid transition zone. By means of field investigation， remote sensing image interpretation and sediment particle size analysis， the blocking effect of the upper reaches of Wuding River on the eastward advance of Mu Us Sandy Land is analyzed. The results show that： （1） The geomorphic map of remote sensing image interpretation shows that the west side of the river is mainly mobile and semi mobile sand dunes and fixed sandy land， and the east side of the river is close to the river， with some sand covered areas， Then eastward， it is transformed into hilly area dominated by sand loess and loess. （2） The particle size analysis of surface samples collected on both sides of the river shows that the particle size of samples on the west side of the river is 100-200 μm， and the particle size of the sample on the east side of the river is less than 100 μm， indicating that it is difficult for coarse-grained aeolian sand to leap over the river channel with a certain width， blocking the continuous extension of the desert to the east. （3） Some main streams and tributaries in the upper reaches of Wuding River have a significant blocking effect on the eastward advance of wind sand. The blocked river sections are mainly distributed between Leilongwan Town and Yuhe Town in the main stream and Luhe River， an upstream tributary. The formation of this phenomenon is the result of the long-term action of wind and water power in the study area. The background is the transformation from drought to wetness， which has not only geographical causes， but also aeolian sand dynamics causes. The demonstration of this phenomenon has enlightenment significance for the understanding of landform in the transition area.