Power system emergency control based on contingency detection and pre-decision-making can take into consideration some well-defined but extremely severe contingencies specified as the third level in the Guide on Security and Stability for Power System， however， it cannot replace the third defense line. A complete solution for adaptive islanding control of large complex power systems is an out-of-step islanding control system based on system design concept and global real-time information. Besides， the mechanism and criterion of islanding control when interconnection lines are not located at the oscillation center as well as the islanding control technology aiming at preventing frequency and voltage collapse of a large receiving end system should also be studied. The paper presents a hierarchically distributed control system-adaptive islanding control system（AICS） to meet the islanding requirement of modern power systems in the case of oscillation center shifting and multi-area out-of-step oscillations.