Abstract: Unused land is not only an important land resource reserve, but also an important part of the ecosystem. Unused land plays an important role in easing land supply and supporting ecological stability. However, the ecological importance of unused lands has not been given due attention. Studies on unused lands have mainly focused on the evaluation of the suitability for exploitation as arable and construction lands. Most of the studies have failed to give enough attention to the ecological value of unused lands. This study used Guyuan County in Hebei Province (a transition ecotone between agriculture and animal husbandry with severe ecological problems) to assess the importance of construction and protection of ecological environment. The recognition of ecological importance of unused lands was not only important for the development of unused lands, but also for the construction of ecological environment in Guyuan County. Based on the ecological conditions in Guyuan County, the study used disaster protection, human interference and habitat and water protection as indicators to determine the ecological importance of unused lands. Combined with spatial analysis in GIS and the spatial strengths of the indicators of ecological importance, the study determined the ecological importance of unused lands in Guyuan County and grouped the lands into 4 categories ― very important, important, relatively important and less important. Based on terrain features of Guyuan County, this study divided the elevation and slope factors into 4 zones each (1 2001 400 m、1 4001 600 m、1 600 1 800 m and 1 800 m in elevation; 0°5°、5°15°、15°25° and >25° in slope gradient), which were used to analyze the characteristics of unused lands ecological importance in different terrain gradients. The results showed that the areas of unused lands with very important, important, relatively important and less important levels were respectively, 11 082.78 hm², 11 209.05 hm², 11 450.25 hm² and 4 803.12 hm², and accounting for 28.75%, 29.08%, 29.71% and 12.46% of total unused land in Guyuan County. The area marked as less ecological importance was low. According to the analysis on the base of terrain factors, unused lands were mainly distributed in the 1 400–1 600 m elevation zone and the 0°–5° and 5°–15° slope zones. The unused lands in Guyuan County with very ecological importance were mainly distributed in the 1 400–1 600 m and 1 600–1 800 m elevation zones and the 5°–15° slope zone. With increased elevation and slope, the proportion of unused lands with very ecological importance changed greatly, increasing from 11.31% to 97.95% and from 13.86% to 93.64%. Most of the unused lands in Guyuan County were important for the ecology and there was the need to pay keen attention to the ecological environment when using the unused lands. These results provided scientific guidance to the development of unused lands and the construction of ecological environment in Guyuan County.