Based on the characteristics of three-phase symmetrical fault development of UHV transmission lines and detailed analysis of three-phase symmetrical fault phase selection requirements， an adaptive three-phase symmetrical fault selecting element was proposed in this paper. By using three-phase current variation， according to zero sequence components， the settings can be adaptively selected to determine whether there exist three-phase current variations， and if so， whether they are equal. The impact from transient component can be reduced to achieve fast and accurate fault phase selection. The fault phase selection principle is not affected by transition resistance. It has been proven by analysis that the phase selecting element proposed is better in three-phase symmetrical fault selection than conventional method using phase current differential variation. Theoretical analysis and simulation test of the protection shows the effectiveness of the method proposed in this paper.