A regional differential protection device for the reaction phase to phase fault of the distribution network was designed, as a result of failure to swiftly, efficiently and accurately identify, locate and eliminate the reaction phase to phase fault of distribution network. The device is installed at each bus bar. Each incoming and outgoing data information of the bus bar is read through the RS485 bus, the communication between each regional protection device is achieved through the optical fiber connection, and the regional protection device with the most hierarchical lines on the bus bar is the host station. Exchange the real-time operation data of the line collected by the regional differential protection device in the lines between the regional differential protection devices, the regional differential protection device begins to execute identification and send fault information to the host station to composite the fault information matrix A when detected single-phase current sudden change is greater than the set value. In result, swift, efficient and accurate detection of distribution network fault, furthermore, isolation of phase to phase fault are achieved.