Research conclusions:(1)Urban rail transit power supply system which takes lightning overvoltage protection measures could reduce the breakage rate of OCS insulator after thorough flash-over in overvoltage，also reduce the tripping rate of substation in a lightning stroke，which could meet both the reliability requirement of tractive power supply system and safety requirement of operation. (2)Because the protection measures to the isolator are inadequate，lightning arrester could not prevent backward flashover tripping, severe accidents and damages occur.(3)OCS insulator has low lightning withstand level，it is a valid measure to install in parallel metal oxide arrester with gap to prevent insulator lightning stroke damage. (4)OCS steel mast shall be earthed and OCS shall be installed overhead earth wire and shall approach live conductor as possible as it can，but no need to lift. (5)The substation shall adopt corresponding measures to carry out overvoltage protection against lightning stroke.(6)The research result can be applied on urban mass transit rail aspect.