A zero-sequence current differential phase selection element based on a three-sequence differential currents similar principle is proposed.The electric characteristics of three-sequence differential currents in different grounding faults of transmission line are analyzed with phasor diagram.For single-phase-to-ground fault，magnitude and direction of three-sequence differential currents of fault phase are the same，and according to this，three-sequence differential currents are compared to identify phase of single-phase-to-ground fault.And zero-sequence differential current in phase selection criterion（PSC）is selected as polarization quantity.Then acting area of PSC is adaptively adjusted，in order to ensure that PSC will not act when two-phase-to-ground fault happens.Real time digital system（RTDS）simulation results show that it is same as theory analysis，and the sensitivity of phase selection element is high.The phase selection element is immune to load current and is able to correctly identify fault phase of single-phase-to-ground.