Abstract: The capacity of water-soil affects directly the sustainable development of social economics. This paper dissertated systemically the basic principles and methods of water-soil capacity, combined the characters of the water- soil resource with the economic development, and built the systematic model of water-soil capacity by applying the theory and method of systematic dynamics in north west arid. With the model, this article analyzed systemically the water-soil capacity in HEXI corridor. Through the analysis of natural resources in Hexi area, including the analysis and evaluation of climate resources, land resources and water resources, we make out the feasibility of the agriculture in this area, the status quo of water and soil resources utilization and its potential of further utilization, then we can ascertain the standard of three input scheme. According to the analysis of real productivity, as the gist of productivity in the year of different level, we can calculate the theoretical potential productivity, and evaluate the biomass of the whole area, and then we can make out the water resources carrying capacity of population. Meanwhile, with the analysis on national population policy, we can find out the trend of population change in the future through the analysis on the population changes. Comparing the future population and the water resources carrying capacity of population, we can make out the potential capacity of population, so as to put forward the countermeasures under the premise of proper development and utilization on water and land resources in this area. As can be conclude from the analysis, there is some potential of the water and soil resources carrying capacity in Hexi area, and then put forward the measure and countermeasures of advancing the water-soil capacity.

Key words: Northwest arid Area, Systematic dynamics, Water-soil resource, Water-soil resource capacity