The spatial and temporal variability of the soil moisture status gives an important base for the assessment of ecological (for forest restoration) and economic (for agriculture) conditions at micro- and meso-scales. It is also an essential input into many distributed hydrological models. However, there has been a lack of effective methods for its estimation at the landscape scale in the study area. The objective of this study is to model the variability of the soil moisture regime in the southern Qilian Mountains with an area of 10,009 km 2 . First, a small catchment named Pailugou catchment (area of 10 km 2 ) is selected. A modified wetness index, including the topographic wetness index, solar radiation and the monthly mean precipitation, is developed. Based on GIS-assisted regionalization of parameters, the soil moisture status at the grid scale of 1×1 m 2 can be estimated using the modified wetness index in Pailugou catchment. Secondly, we validate the method with a collection of 15 points within the small catchment. The results show that soil moisture status estimations are significantly improved of using the modified wetness index.