Abstract: Performing line commutation at an appropriate distribution switch can better balance the inductive reactance between three-phase lines and reduce transmission line losses. However, due to the large number of distribution lines and the complex operating environment, the management of distribution line is very difficult, and after the commutation some distribution lines are in negative sequence operation because of failing to plan reasonably and no checking phase sequence in time, that affect the normal operation of the feeder terminal unit(FTU). This paper first analyzes the FTU’s working principle of the dual power supply, then studies the FTU’s protection function configuration, and then obtains the influence of negative sequence operation of the line on the power supply and protection of the FTU. At the same time, according to the negative sequence operation characteristics of the line, this paper puts forward some suggestions, such as adding phase sequence alarm function, phase adjustment of the access device through software adjustment, self-adaptation of the power supply, etc.in order to improve the low efficiency management to find and resolve the negative sequence operation of some distribution lines. Finally, combined with a negative sequence operation case at some place in Shandong Province, it is verified that the negative sequence operation of the line can affect the operation of the FTU and the proposed method can effectively improve the distribution line management efficiency and the reliability of the FTU.