Abstract: This paper presents the approaches and principles for building design and decision expert system of land rational use (DDES). The system can be used to evaluate and decide the plan on the geo expert level for the rational use of land. Furthermore, several practical suggestions can be obtained by consulting the system, so that the users can select an effective plan for utilizing the land. By citing the formulation of the DDES of the Urumqi River basin as an example, the author expounds the method to express expert knowledge of planning and decision for rational use of the land in the basin as well as the basic rules to express the knowledge contained in the expert system and the organization modes of expert knowledge in the knowledge base. In addition, the author discusses the design principles and organization method of inference rules and the inference algorithms.

Key words: land rational use, expert system, knowledge base