A novel selective leakage protective device in master-slave structure was proposed where dsPIC30F4012 was the master controller and PIC16F877A was the slave processor. The device used the principle of additional DC power supply in main feeding switch to examine the occurrence of the leakage and used the principle of direction of zero sequence power in branch feeding switch to judge the faulty line. The hardware diagram and the software flow chart of protective system were given and RS-485 bus and optical fiber communication technology were adopted. It could improve the action capability and anti-interference capability of the leakage protective device for power supply system in underground, and the experimental results confirmed the protection device proposed had good performance.