Abstract: Since off-grid wind power-to-hydrogen (Wp2H) systems are not connected to the utility grid, the hydrogen production load and the energy storage system (ESS) must be coordinated to absorb wind power fluctuations and maintain system stability. Such coordination must consider the flexibility constraints of hydrogen production units, the overall hydrogen yield, and the degradation of batteries in the ESS to meet the economic goals of green hydrogen production. Therefore, an optimized bi-level control method for the active power balance is proposed. Firstly, using the Itô process to characterize wind power fluctuations and considering the real-time flexibility reserve of multiple electrolyzers, the upper level is formulated as an intra-day scheduling problem with a 15-minute resolution. Secondly, the lower level optimizes the real-time power of the electrolyzers and the ESS based on their on-off states and baseline power commanded by the upper level, considering the degradation cost of the ESS. This helps to absorb second-level wind power fluctuations. Finally, based on a project plan in Inner Mongolia, China, a case study verifies the effectiveness of the proposed method.