Based on distributed artificial intelligence technology, the paper proposes a distributed expert system for distribution system planning. The developed expert system is made up of a set of problem-solving agents that autonomously process local tasks and cooperatively interoperate with each other by a shared database in order to reach a proper distribution plan. In addition, a two-level control mechanism composed of local-control and meta-control is also proposed to achieve a high degree of goodness in distribution system planning. To demonstrate its effect, the distributed expert system is implemented on basis of NASA's CLIPS and SUN's RPC and applied to the planning of distribution system in Taiwan. Test results indicate that the distributed expert system assists system planners in making an appropriate plan.