In order to explore the influence of grounding system defects such as lead seal defects on terminal voltage and current of high voltage cable terminal, this paper uses lumped parameter circuit to establish RLC equivalent model of lead seal terminal. Based on COMSOL, the terminal capacitance parameters and experimental test resistance parameters are calculated, and the variation characteristics of terminal voltage and current under defects are analyzed and verified by actual fault cases. The results show that the fracture of the lead seal leads to the unreliable connection between the aluminum sheath and the tail pipe, resulting in the voltage suspension of the terminal aluminum sheath, and the long-term operation will cause the discharge between the aluminum sheath and the buffer layer. The interlayer defect of lead seal leads to the decrease of contact area between aluminum sheath and lead seal, and the minimum allowable contact area at lead seal is about 10%. The research results can provide a basis for the diagnosis of lead sealing defects in high voltage cable terminals.