Extruded high voltage direct current（HVDC） cable is the core equipment for a flexible HVDC transmission and a physical basis for the construction of direct current（DC） power grids. The space charge problem in insulating material is a key technical problem that restricts the development of extruded HVDC cable

and it is also a hot research point in the field of electrical insulation. The study of the temporal and spatial evolution and the related mechanism of electric conductivity

electric field and space charge under the electro-thermal coupling field is the theoretical basis for solving the space charge problem. Consequently

from two aspects of space charge formation and space charge suppression

we discuss and analyze the space charge formation process

the relation between the space charge and the electro-thermal coupling field

the method and principle of the insulation and shielding material modification and space charge suppression mechanism in the HVDC cable insulation. Finally

we make a prospect to the future research tends of space charge in HVDC cable insulation

and point out that impact assessment and aging mechanism research of the long-term space-time evolution of space charge under electro-thermal coupling field on insulation aging of DC cable and matching control of insulating material characteristic parameters are of great significance to the development and long-term reliable operation of HVDC cables.