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Scale problem is one of the core problems of landscape ecology, ecological spatial network is spatially represented as the mosaic of ecological source patch, ecological corridor and matrix landscape. Therefore, it will also be affected by the scale effect. Taking Dengkou County in the northeast edge of Ulanbuhe desert as the research area to study the grain-size effect of county ecological spatial network. The results showed that the change of grain-size had an obvious impact on the spatial and topological structure, area of ecological sources and spatial distribution of ecological network. But the grain-size effect of ecological resistance surface was not obvious. With the increase of grain-size, the area of ecological source patches fluctuated obviously and its shape became more and more broken. The length of ecological spatial network was increased at first and then decreased, its spatial distribution was changed from continuously dense to gradually sparse. The topological structure indexes of the ecological network was changed obviously. With the continuous increase of grain-size, the degree distribution of the network became more centralized, homogeneous, hierarchical and modular, the heterogeneity of the network continued to improve, the connectivity continued to decrease, and the overall changes trend were in a more unstable direction. This research showed that grain-size effect must be considered in the study of ecological spatial network. However, the causes of this effect and the method of selecting the optimal scale still needed further study. The research result can provide reference for the selection of research scale in relevant researches and the designation of county ecological protection measures.