Given the strategic development of industry and economy over northwest China, the ecosystem over the region will dramatically change. In particular, an increasing proportion of the land is expected to be covered by vegetation, including grass, trees and crops. At the present, most of the region is in desert or semi-desert conditions, where vegetation is very sparse and precipitation is low. A serious issue is the sustainability of vegetation: will the future regional climate conditions favor the maintenance of the vegetation under managed or unmanaged environments? As an initial step, a high-resolution regional climate model (RCM) is used to study the climate responses to an extreme case, where the dominant land cover over Xinjiang, currently barren or sparsely vegetated, is all replaced with grasslands. The simulations show that, in response to the grassland replacement, Xinjiang summer mean precipitation will increase, surface air temperature will decrease, and surface soil wetness will rise. In addition, the diurnal range of precipitation (temperature) will be enhanced (reduced). These changes result mainly from the increased surface evaporation which in turn is attributed to the enhanced surface water availability (greater green vegetation cover and wetter soils) for regional recycling, while the surface albedo and roughness effects are relatively small. The resulting climate responses tend to favor the grasslands to naturally grow in and be adapted to the new regional environment over Xinjiang. On the other hand, precipitation will decline over the Inner Mongolia, which is particularly damaging since the regional grassland there is currently China’s main pastureland and is experiencing dramatic desertification. The uncertainty in the credibility of the RCM results, however, warrants further comprehensive studies, where an interactive ecosystem and global climate changes must be incorporated.