The possible characteristics of out-of-step oscillation of multi-section and multi-channel interconnection power grid are summarized and analyzed, such as the selectivity of multi-section out-of-step, the different out-of-step time of different channels on the same section and the lack of obvious out-of-step characteristics of some channels on the same section. In response to the problem that the existing local out-of-step splitting schemes can′t adapt to the above characteristics, a wide area out-of-step splitting control system method based on the action permission command of local splitting device and constructed through remote communication is adopted. A wide area out-of-step splitting control system of China Southern Power Grid is designed and established with the main principles of considering solving the problem of the existing local out-of-step splitting scheme, the coordination with the existing local out-of-step splitting function, system error prevention design and the control strategy processing logic under abnormal circumstances. The real-time digital simulator （RTDS) simulation test results show that the system can respond correctly, selectively, quickly, and reliably take established measures to split the related sections at the same time, effectively solving the limitation of the existing local out-of-step splitting scheme and meeting the operational needs of actual power system.