The failure rate of 10kV existing line arrester is high, in order to improve the operational reliability of line arrester, a 10kV externally gapped line arrester is designed. In order to determine the shape of the discharge electrode and the distance between the upper and lower electrodes of the lightning arrester, the potential and electric field distribution of the lightning arrester body were simulated and analyzed in COMSOL software. The simulation results show that for the same electrode, as the electrode radius increases, the electric field will decrease in the form of a quadratic function. As the electrode spacing increases, the electric field will decrease linearly. The selection of ring electrode or rod electrode can meet the requirements, and the processing of ring electrode is more convenient. The selection of ring electrode is determined, and the electrode spacing is 52 mm through 50% lightning impulse discharge voltage test.