应用系统动力学理论建立了陕晋黄土丘陵区土壤侵蚀发展动态的SD模型。对该区3种治理模式--加速治理型、传统经营型和稳步发展型进行仿真研究，预测到2040年土地利用与土壤侵蚀的长期动态变化。结果表明：土壤侵蚀过程与土地利用和治理强度密切相关，轻度与中度侵蚀面积有明显的滞后增加趋势，即侵蚀过程的“长波”现象。加速型模式是促进该区农业发展生态环境良性循环的最佳模式。

Soil erosion in the loess hills of Shaanxi and Shanxi Provinces is extremely serious, caused mainly by unreasonable land use. This study is the first attempt to use system dynamics theory to simulate the changes of land use and soil erosion in a large region. The system dynamic model used in this study contains 35 flow level equations, 70 flow rate equations, 185 subsidiary equations, 45 table functions and 196 parameters. The model consists of six sub models, each interacting with the others. Through the feedback loop they are connected with all variables and parameters. The functioning of the model depends on feedback mechanisms. The model was run on a PC computer with the software of PD (Professional DYNAMO) Plus. The period of simulation is from 1980 to 2040. The results were tested using collected data for 1980～1990. The efficiency of the model is 91 5%. The model was used to simulate the dynamic changes in soil erosion in three different types of land use management programs through 2040: intensified management, traditional management, and steady development management. The simulation results of the three types of programs were analyzed by a comprehensive evaluation method using fuzzy and multi objective targets. The main conclusions of the study are: First, in the loess hills, land use for farming, forestry and animal husbandry changes in a nonlinear dynamic fashion and they affect one another. Thus the adjustment for land use structure should be made gradually to maintain dynamic balance. Different types of land use should be balanced. Second, land use pattern is the key factor affecting soil erosion. Reasonable land use and effective management can reduce erosion to a minimum. Otherwise soil erosion will intensify and the overall land use benefits will decline. Third, the levels of soil erosion in the region vary from slight, moderate to severe, and the rate of erosion is related to land use pattern and the intensity of land use management. There has been an increase in slight and moderate erosion in the recently developed land due to intensified human activities in the contemporary period. Soil erosion can be reduced to a minimum but it can never been stopped completely. Fourth, intensified management is the best approach for a balanced development of farming, forestry and animal husbandry and for sound ecological equilibrium in the region.