Pilot zero-sequence directional protection has been applied successfully to the relay protection in UHV transmission line. The basic principle of zero-sequence directional element determines that it can only react to the grounding fault but can’t react phase to phase fault and symmetrical fault, this paper takes out a way to solve this question. Zero-sequence directional element improvement is that using the data window delay and logic choice together to give the correct judgment of the phase to phase fault and symmetrical fault. The improved zero-sequence directional element not only can correctly reflect the grounding fault, but also can take a very good reaction for the three phase fault and phase to phase fault. And a lot of theoretical analysis and simulation on the improved zero-sequence direction element proved that it can work correctly and its application in UHV transmission lines is very good.