Abstract: In response to the lightning protection requirements of transmission lines above the altitude of 4000 m in the Ngari power interconnection project, the parallel gaps of 110 kV and 220 kV insulators are designed and trial-produced. The parallel gaps of each level are designed according to 85% and 90% of the length of reference insulator strings. In order to verify the performance of the parallel gaps in high altitude areas, a lightning impulse characteristic test is carried out at the High Altitude Tibet Test Base of the State Grid. 110 kV, 220 kV ceramic insulator strings and different types of parallel gaps are tested and studied. The lightning impact 50% discharge voltage, volt-second characteristics and protection effectiveness of parallel gap protection are tested. Experimental results show that all types of parallel gaps can effectively protect the insulator string from arc ablation. The parallel gap volt-second characteristic curve is required to be reduced by more than 10% compared with the insulator string. Therefore, the 85% gap type is suitable for the 110 kV voltage level. Moreover, both two parallel gap types of the 220 kV voltage level can meet the operating requirements.