Abstract: With the rapid development of deep and distant offshore wind power, the transmission and the grid integration of wind power via HVDC systems have become technical hotspots. Focusing on several vital technologies such as AC collection-based DC transmission, low-cost DC transmission, multi-terminal DC transmission and multi-voltage-level DC transmission, the paper comprehensively discusses the current status, existing problems, research hotspots and development trends of the offshore wind power via DC transmission technologies in terms of system topology, equipment, control and protection. It is pointed out that the transmission and grid integration of offshore wind farms via the centralized HVDC system is the mainstream scheme in the near future. For such a system, the broadband oscillation is an urgent problem to be solved, it is the focus of attention to make the whole system perform the characteristics of dominant power sources. In terms of cost reduction, the technical route of the diode rectifier based HVDC transmission system has good features. However, to use pure diode rectifiers as the sending-end converter requires the improvement of wind turbines. For the multi-terminal DC grid with wind power integration, the development depends on the progress of low-cost DC circuit breaker and transient control and protection technology. And the offshore wind power transmission and grid integration via multi-voltage-level DC grid still lacks the support of the DC transformer and other key equipment.