Abstract: The medium- and long-distance offshore wind farm integration scheme based on grid-forming wind turbines (WTs) and the diode rectifier unit (DRU) has technical and economic advantages. Since the DRU must be supported by AC voltage and its power transmission is unidirectional, neither the DRU nor the onshore grid can start the offshore wind farms. In this case, the grid-forming WT can become the black start source for the offshore wind farm. Firstly, the topologies of two DRU-based offshore wind power integration systems are introduced. Secondly, the structure and control strategy of the grid-forming WT are elaborated, and the self-synchronization during the WT start process is analyzed. Then, the reactive power balance of offshore AC system is studied, and the measures to avoid reactive power overload when WTs starts are proposed. On this basis, the black start strategy of offshore wind farms is proposed. Finally, electromagnetic transient simulation models of the DC transmission scheme for medium-frequency grid-forming offshore wind power and the AC transmission scheme for low-frequency grid-forming offshore wind power are established in PSCAD/EMTDC to simulate the black start process of the DRU-based offshore wind farm. The simulation results verify the effectiveness of the proposed black start strategy based on the grid-forming WT.