During the process of the interactive frequency regulation between offshore wind farm and island microgrids, the sufficiency of the inertia level of island microgrids is in a time-varying state, which will seriously affect the stability of microgrid running after the faults, such as the tie-line interrupt. In order to ensure the safe and steady operation of island microgrids in the process of the interactive frequency regulation, this paper further proposes the interactive frequency regulation strategy which takes minimum inertia requirement into accout on the basis of the interactive frequency regulation strategy between offshore wind farm and island microgrids. Firstly, based on the national demonstration project of Wanshan island renewable energy microgrid in Zhuhai, the assessment system of minimum inertia requirement of island microgrids is built. Secondly, minimum inertia requirement of island microgrids is solved by genetic algorithm and particle swarm optimization（GAPSO）. The stability margin of the inertia supporting of the island microgrids is refined. The inertia control level of island microgrid on offshore wind field is constrained. Finally, the frequency response characteristics of island microgrid are analyzed under severe disturbance and faults by the example simulation.