In order to produce cable with high insulation, plenty of modifying agent shall be added to improve its electrical performance. Kaolin can be a kind of very good raw material used to produce modifying agent for electrical performance. After properly burning, the burned Kaolin can achieve super high insulation ratio. The burned Kaolin at different temperatures can achieve different clearance ratios. The clearances in cable can absorb some active harmful materials so as to improve the insulation of cable.