Abstract: Research purposes: In order to meet the reliability and flexibility of power supply in railway junction area， large station and railway branch line， sub - section post of direct supply is usually set to expand feeding lines for independent power supply unit. Circuit breakers that are located at feeding lines of switching station and incoming lines of switching station and feeding lines of traction station form a multi - level protection. The research finds a more reasonable and more reliable protection scheme to solve the problem of overstepping trip) due to poor protection in the actual operation. Research conclusions:( 1) In view of tlie current development situation of relay protection device，it is proposed that tlie range of protection coordination should be reduced to 0. 2 second from 0. 3 second. (2) Two protection schemes are put forward according to relative position of substation and sub - section post. (3) Solutions of short circuit near substation and bus short circuit in sub - section post after protection adjustment are raised. (4) The research conclusion provides guidance for the protection setting and the setting calculation of substation and sub - section post，to give the guarantee of improving the reliability of power supply and reducing the scope of power cut and the time of power cut.