With the continuous development of offshore wind energy, offshore wind farm voltage problem of the system of safe operation is extremely important, and reactive power compensation problem affects system quality, therefore, restriction on the voltage should also be considered in determining the scheme of reactive power compensation. Basing on the offshore wind farm with overhead lines and submarine cable hybrid transmission lines of wind electric field electromagnetic transient model, this paper proposes a method of reactiv power allocation scheme for offshore wind farm access system considering power frequency overvoltage by using ATP / EMTP simulation software to calculate the offshore wind farm power frequency overvoltage, and on this basis to calculate the wind power capacity requirements to get range for the safe operation of the system of offshore wind farm with configuration scheme of reactive power capacity. Taking a certain offshore wind farm as an example, the power frequency overvoltage and reactive power compensation are calculated and analyzed. Finally, the feasibility of the proposed scheme is verified by MATLAB/Simulink simulation.