As there are large number of phase conductors of multi-circuit transmission line on the same tower, the parallel gaps configuration for the line is complicated and different configuration mode exhibits different lightning performance. Combined with double-circuit and triple-circuit transmission line on the same tower of Guangzhou Power Supply Bureau,optimal parallel gap configuration scheme for lightning performance of multi-circuit transmission line on the same tower is proposed based on analysis of lightning impulse characteristics of insulator strings and lightning protection performance, meanwhile, the lightning protection validity of parallel gaps is also studied. The results show that the lightning impulse 50% flashover voltage of long insulator with parallel gaps is about 80% of that without parallel gaps, and the voltage-time characteristic curve of long insulator with parallel gaps is under that without parallel gaps. The two aspects both indicate good insulation coordination between parallel gaps and insulator. The lightning impulse flashover arc can be led to the air formed by parallel gaps till extinction which proves effective protection of parallel gaps for insulator against lightning. It can be concluded as well that unbalanced insulation configuration between circuits formed by parallel gaps plays an effective role in reducing the lighting simultaneously trip-out rate of multi-circuit transmission line on the same tower.