[Objective] High voltage direct current system is a common scheme for far-offshore wind power and has already been implemented in practical engineering projects. But this scheme is still facing the problems of high cost of offshore converter station platforms and large losses in the collector system. To address this problem, this paper investigated the optimal frequency selection for the far-offshore wind power medium frequency gathering system. [Methods] Firstly, finite element modeling was used to accurately calculate the distribution parameters and current carrying capacity of submarine three-core cables at different frequencies. According to the calculation results, referred to the wiring scheme of similar scale offshore wind farms for the selection of submarine cables. Then, the power losses in the collector system and the losses in the offshore diode rectifier platform were calculated, and converted the losses to the price of electricity. Finally, the optimal operating frequency of the offshore wind power high voltage direct current transmission system was selected by integrating the economic analyses of submarine cables, collector losses and offshore converter platforms. [Results] The increase in operating frequency would increase the investment cost of the collector system and the loss of the converter platform, would reduce the investment cost of the converter platform, and the optimization of the submarine cable selection could prevent the excessive increase in the investment cost of the collector system. [Conclusion] In this paper, the economic analyses of submarine cables, collector losses and offshore converter platforms are synthesised to conclude that the optimal operating frequency of the offshore wind power high voltage direct current system is 180 Hz, which achieves a good balance between technical feasibility, cost-effectiveness and operational efficiency.