The invention discloses a section out-of-step splitting discrimination control system. The system comprises a master station and a plurality of substations. Each substation comprises an acquisition module for acquiring current and voltage data of an outgoing line; a logic discrimination module which performs out-of-step discrimination according to the current and voltage data; a first sending module which sends the out-of-step state of each line to the main station; an action outlet module which receives and executes a splitting instruction of the main station. The master station comprises: achannel out-of-step determination module, which determines the out-of-step state of each channel according to the out-of-step states of all lines; a section out-of-step judgment module which judges the out-of-step state of each channel and a preset section out-of-step judgment channel number constant value to obtain a section out-of-step state; a second sending module which sends a splitting instruction to each splitting station. The substations are deployed at two sides of each channel of the section, the current and voltage values of all lines are collected and out-of-step judgment is carried out, and the problem that an out-of-step splitting device cannot act due to oscillation center migration is solved; a channel number constant value is judged through open section out-of-step, and the system is flexibly suitable for various operation net racks.