Abstract: The development of high voltage direct current（HVDC） grid is an effective approach to implement the large-scale long-distance power transmission, the large-scale renewable energy integration and accommodation, and the safe and stable operation of the interconnected AC grids. This paper reviewed the latest research progresses of DC transmission technologies, summarized the characteristics of DC grid, and discussed the current research status of DC grid. Then a typical topology of HVDC grid considering the integration of large-scale renewable generations over different regions was proposed. The technical requirements of such a HVDC grid was studied and refined accordingly. Furthermore, new types of key equipment, new control and protection technologies, reliability evaluation methods and standard system of such a HVDC grid were analyzed and the present research foundations and the future research directions of these relevant technologies were stated. It provides a technical reference for future research and construction of the DC grid in China.