Directional pilot protection principle, which is based on voltage and current fault components, is used in AC transmission lines widely. However, comparing to general AC transmission lines, the AC transmission lines which is connected to LCC-HVDC inverter station have different fault characteristic and the adaptability of directional pilot protection should be analyzed. Firstly, the effect of three different working status of inverter station (no commutation failure, single commutation failure or continuous commutation failure) on directional pilot protection is analyzed. Secondly, the effect of three different AC transmission line structures connected to inverter station (single transmission line, several single transmission lines or double transmission lines) on directional pilot protection is also analyzed. Eventually, ±800 kV Tian-Zhong LCC-HVDC transmission system (including 500 kV AC transmission system connected to inverter station) simulation model is established based on PSCAD and the simulation results prove the correctness of theoretical analysis. This work is supported by National Key Research and Development Program of China (No. 2016YFB0900603).