Abstract: In HVDC cables, the interface morphology between insulation and shielding will cause electric field distortion. This is one of the reasons of cable insulation faults. Such morphology is related to the carbon black particles added in the shielding. In the process of cable production, these carbon black particles may enter insulation, form bulges on the interface, and thus cause electric field concentration. In this paper, the above mechanism is considered. Geometric model of such morphology is established based on stochastic process. Finite element method is used to solve electric field distribution near the interface. Electric field distortion caused by interface morphology is studied from the aspect of statistics. As results show, to reduces such distortion, one of the most effective methods is increase carbon black particle diameter or reduce the depth of particle entry. If there are small and unremovable particles in the shielding, it is recommended that big carbon black particles should be added.