When a substation is struck by lightning, it will cause the ground potential to rise, which will further cause serious interference to the secondary cable. This article is based on the grounding grid established in the testing ground. The grounding copper bar is laid in the cable trench to connect with the grounding grid. At different grounding grid points, use a lighting current impulse generator to apply high current. At the same time, the grounding grid model is established by using the ATP-EMTP software. Through the combination of test and simulation, the influence of different lighting inflow locations on the protection effect of grounding copper bar is studied, and combined with the connection method of the grounding copper bar and the grounding grid, the protective effect of the grounding copper bar on the secondary cable under the impact of lightning current was analyzed. The research results showed that the laying of grounding copper bars can reduce the influence of interference voltage on the secondary cables under certain circumstances, but when there are multiple connection points between the grounding copper bar and the grounding grid, the current injection position is different, which will affect the voltage between the cable core and the shielding layer. At the same time, it will also affect the ground potential rise of cable grounding point in different degrees.