Abstract: The diode rectifier unit can improve the economy and reliability of the long-distance large-capacity offshore wind power DC transmission system. This paper presents an optimal configuration method for AC filters in offshore wind power integration systems based on the 24-pulse diode rectifier unit.Firstly, the structure of the offshore wind power transmission system based on the 24-pulse diode rectifier unit is defined,and the basic principle of the 24-pulse diode rectifier unit is expounded. Then, the reactive power requirement of the 24-pulse diode rectifier unit is calculated. For the 24-pulse diode rectifier unit, the complicated AC filter can be simplified into a capacitor. By scanning the filtering effect of capacitors with different capacities in the range of active power variation, the reactive power capacity optimization method of the capacitor is proposed, which takes the filtering effect and the filter capacity into consideration. Finally, in PSCAD/EMTDC, the harmonic analysis and AC filter optimization design of the offshore wind power test system based on the 24-pulse diode rectifier unit are carried out.