The feeder busbar joint system is an important component in the International Thermonuclear Experimental Reactor (ITER) project. The insulation materials for the feeder busbar joint play a crucial role in both mechanical support and high voltage insulation. The G-11 block, which is a kind of industrial high-pressure, glass-reinforced epoxy laminates, has been chosen for the feeder busbar joint as insulation and mechanical support. The electrical characteristics of the G-11 depend significantly on temperature. As the feeder system works at the temperature of 77K, to ensure safe operation, the DC flashover voltage is required to be studied in a cryogenic environment. In this work, DC flashover characteristics of the G-11 at both room and cryogenic temperatures have been investigated using a self-developed test system. The results show that the surface flashover voltage rises as the flashover times increase. In addition, results indicate that the flashover voltage of the G-11 depends on orientations and it increases as the temperature decreases.