Abstract: By observing and analyzing the sparking and breaking down of the high-voltage cable socket of the pulsed power supply during the 72 hours conditioning experiment, the electrical field distribution equivalent circuit of the terminal of the high-voltage cable was built, the formula of the potential difference from the cable-terminal to the metal shielding layer was conducted. The reason of breakdown is analyzed theoretically in this paper. It is suggested that the un-chamfered insulation of the cable-terminal causes space charge focusing, which then results in a temperature increase leading to the high-voltage cable socket breakdown. The theoretical analysis is proved by the position of the breakdown hole of the high-voltage cable socket. The handling method of insulation of the cable terminal is presented, which was validated by continuous conditioning experiment for 72 hours.