The natural restoration of land used for engineering construction is the important to restoration of damaged grassland ecosystem in the Qinghai-Tibet Plateau. In July and August of 2011, a field survey was conducted to determine the effect of areas of land used for engineering construction on features of restorable plant communities in the alpine steppe regions of the Qinghai-Tibet Plateau by investigating the plant community composition, spatial structure, plant diversity, aboveground biomass and calculating the restorable capacity. This study showed that the dominant species and associate species of restorable plant community varied with the decrease of areas of land used for engineering construction, indicating that the Stipa purpurea was sporadically found in the restorable plant communities when the area of land used for engineering construction was 156 m², and became the main associate species when the area of land used for engineering construction was 55 m². As the areas of land used for engineering construction reduced, the height, cover, α diversity index and aboveground biomass increased, in which the height, α diversity index and aboveground biomass of restorable plant communities was close to those of undisturbed plant communities when the area of land used for engineering construction was 156 m², and the cover of restorable plant communities was close to that of undisturbed plant communities when the area of land used for engineering construction was 55 m². The β diversity index decreased and the restorable capacity increased with the decrease of area of land used for engineering construction, indicating that the smaller area of land used for engineering construction was advantageous for the natural restoration of plant communities. This study suggested that the responses of restorable plant communities to land used for engineering construction with the size of 156 m² were more sensitive than that at other areas of land used for engineering construction from plant species diversity, biomass, height, and restorable capacity.