Abstract-Electric field distribution in cable joint can be enhanced because its structural complexity, this forms interface discharge between the main insulation of cable and the insulation of cable joint. Polypropylene (PP) has good electrical property and is suitable for being used as insulation material of power cable. On the other hand, silicone rubber (SiR) has been widely used as the insulation of cable joint. The interface between the PP and SiR becomes a weak point where an discharge phenomena may be introduced. In order to improve the electrical property of the interface, a corona discharge treatment has been employed in this research, by which the surface chemical and physical structures of PP can be modified. Obtained results showed that with the treatment of AC corona, the interface breakdown time was obviously extended. It is suggested that the interface breakdown strength can be enhanced through the corona discharge treatment method.