Desertification is one of the most serious environment and social economic problem nowadays in the world. Desertification causes extensive concern of international academia for its development speed and serious calamity. It’s very significant to study quantitatively the relationships between desertification driving factors and desertification

and to build up dynamic simulation model to predict the expansion of desertification. This paper states how to build up desertification dynamic simulation model based on the cellular automata theory using 3S technology. The design of model based on grid data and embraced two parts: the layer of desertification distributing

and the layer of combination control factor. There fore

the layer of combination control acting as external environment of model impacts and controls the behaviour of desertification expansion. After analyzing syntheses mechanism of desertification expansion

we established six impact factors of desertification

and established this layer’s weight coefficients of drive factors by using optimized Analytic Hierarchy Process （AHP）. After making certain neighbor configuration and transformation rule

we utilized this model to predict desertification expansion in Beijing and its neighbouring areas. The result of the simulation proves that the model is effective to simulate desertification expansion in terms of macroscopic and microcosmic. According to the research we can say that the desertification has influence on Beijing and its neighbouring areas for a long time

but the desertification expansion mainly occurs in the northern areas of Beijing.