When a permanent fault occurs in distribution systems, the fault location should be detected, isolated and the un-faulted but out of service areas have to be restored. The outage areas can be minimized by the switching operation based on the system load characteristics. By integrating the Outage Management Information System (OMIS), the connectivity of customers and feeder/transformer, the Customer Information System (CIS), the Automated mapping /Facility Management (AM/FM) with the customer load patterns, the hourly load demand and the service priority index of each distribution feeder and each service zone are calculated. By this way, the service restoration of the most power demand and customers can be obtained for the fault contingency of distribution system. To enhance the effectiveness of switching operation for fault contingency of distribution system, the Expert System with CLIPS has been developed by considering the operation rules in the application software program. A underground distribution system with 26 feeders in Kaohsiung District of Taiwan Power Company has been selected for computer simulation to solve the proper switching operation by taking into account the service priority of customers. It has been verified that the proposed methodology can restore the customer power service effectively by Expert System with distribution operation rules.