In view of the practical problem that the internal line of the transmission section may exceed the limit due to excessive load or branch break during the operation of the power system. The calculation method for the active power flow sensitivity (sensitivity of node injected active power to line active power) and comprehensive sensitivity (the sensitivity of the node injected active power to the active power of the transmission section considering the over-limit weight of each transmission section's internal lines) are studied. The particle swarm optimization algorithm is analyzed. The deviation between the actual power and the target power value at the section is selected as the objective function, and the generator’s output are obtained to control the sections. With the IEEE39 network model, the AP clustering algorithm is used to partition the network and to identify the transmission sections. The two control methods are compared and analyzed. It is verified that both methods can be applied to the process of transmission-section control. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 5211UZ18006K).