The section is the weak link of the grid, and the section recognition usually requires a lot of manual calculation, for this limitation, put forward the automatic search method of section section transmission limit chicken swarm optimization algorithm based on Dijkstra algorithm is first used to partition the grid, the contact line between regions as the initial section, according to the OTDF the distribution coefficient and the flow direction of the transmission section from the initial recognition section, in the calculation of the thermal stability limits of transmission section, the power sensitivity matrix based on the generator output power control circuit, maximum power in section under normal operation can transfer as objective function, the section of each line followed by the target on line, the output of generator as control variables, to meet the whole network line thermal stability constraint and the generator, through the optimization method to get off the chickens At the same time, the maximum transmission power limit of each target line is obtained, and the minimum value of the transmission limit of each target line is taken as the transmission limit of section, so that the critical section is obtained. The effectiveness of the proposed method is verified in the IEEE39 system.