Aiming at the abnormal heating of the cable armoring layer grounding line adjacent to the reactor in a 500 kV substation, the models of three-phase reactor, cable armored layer and cable terminal are established, the finite element numerical calculation method is used to analyze the abnormal rise of cable grounding line current and cable terminal temperature. The error between the calculated and measured values of grounding line current is 1.8%, the error between the calculated and measured maximum cable terminal temperature is 3.6%, which verifies the correctness of the model and method, and on this basis, the effect of the magnetic shield on the grounding line current under different placement methods and the heat generation of the magnetic shield are discussed. The results show that laying round and T-shaped magnetic shield at the bottom of the three-phase reactor can effectively reduce the cable grounding current value, and the increase of the magnetic shield area can significantly improve the shielding effect, the magnetic shield will not produce abnormal heat and can be used safely.