Abstract: For problem of low measuring sensitivity of existing phase-sensitive protectors used in low-middle voltage network caused by simple wave logic processing circuit, the paper proposed a design scheme of a novel phase-sensitive protector, and introduced working principle and designs of software and hardware of the protector in details. The protector uses an integrated measuring chip of power-energy parameters named CS5463 to read power factor directly for correct and reliable measurement. The experimental result showed that the protector can act reliably at the short-current moment in 80 ms and the action time of starting and over-loading is more than 8 s, which all meet design requirements.