Abstract: Half-wave transmission is an important method for ultra-high voltage long-distance and large-capacity power transmission. Traditional differential protection is prone to malfunctions. To study the suitable current differential protection, a 1000 kV, 3000 km distributed parameter simulation model is established. The changes in zero-sequence components and differential currents of the line are analyzed based on the fault distance and fault type, and the influence of transition resistance is also analyzed. The results show that the fault location has a significant impact on the amplitude of the differential current. The differential current is larger at both ends of the line, and lower at the midpoint. The zero-sequence characteristics of grounding faults are remarkable. The current differential protection can weaken the interference of distributed capacitance current and has a certain ability to tolerate transition resistance.