The embodiment of the utility model discloses differential protection system for short -circuit fault between the various phases of emergence on protection duplex winding or three circuit transformer winding inside and the lead -out wire also can be used for protecting simultaneously the single -phase turn to turn short -circuit fault of transformer. The embodiment of the utility model provides a differential protection system, include: transformer differential protection system and circuit differential protection system can reduce the quantity of line?protection device, keep outer bridging line operation structure unchangeable simultaneously, avoid appearing transformer high -pressure side trouble mistake and cut the phenomenon of power supply?circuit and bridge circuit breaker and appear.