A new automatic switching method for substation/plant is presented by building the rule tree of the operation task. The process consists in building the operation rule tree with the help of and/or tree according to the operation task， and decomposing it into sub-trees， from which the feasible operation series is extracted to realize the transformation of the status of the specific device from the initial status into goal status. During the study of the extension of the rule tree， such crucial problems as the rule dead-lock， nodes redundancy and nodes conflict are successfully solved， realizing the automatic switching system.