Introduction  With the expansion of the offshore wind farm projects, new power transmission technologies have been widely applicated into the power transfer of the offshore wind farm. The offshore wind farm faces an new challenge which is different from the mature mode of inland power grid, then the different power transmission technologies and development prospect should be further defined.

  Method  This paper summarizes the technical characteristics and development prospect of the four kinds of transmission methods including the offshore wind farm, namely, the high voltage AC submarine cable, the flexible DC transmission technology, the high pressure gas insulated pipe bus (GIL) and the hybrid DC transmission mode; meanwhile, the detailed cost structure analysis and calculation of the various transmission modes are proposed; Finally, economic comparison of different transmission distance from different transmission capacity of the transmission mode is made.

  Result  The results we obtained demonstrate that the current high-voltage AC and DC transmission technology is more mature, and the transmission mode is affected by the transmission distance. The transmission distance is about 52 km as the critical point. AC transmission has economic advantages as the transmission distance is less than 52 km, the cost of AC transmission is equal to DC transmission as the transmission distance is about 52 km, and the cost of AC transmission is less than DC transmission as the transmission distance is more than 52 km, but the transmission capacity has no significant influence on the transmission mode.

  Conclusion  With the different power transmission of the offshore wind farm, AC and DC transmission technology are respectively adoptd from shelf to offshore waters.