Abstract: The global climate change has resulted in frequent extreme storm events in marine areas. Consequently, significant offshore wind power ramps have occurred, thus affecting the safe operation of onshore main grids. Through an electrolysis system, the offshore wind-electrolysis joint system（OWEJS） converts surplus power into hydrogen power, thereby reducing wind-power curtailment rates and penalty costs. Meanwhile, the OWEJS can sell hydrogen power and enhance its economic benefits. This study proposes an OWEJS ramp-control scheme that considers wind-power uncertainties. First, the ramp characteristics of conventional offshore wind farms and the OWEJS under extreme storms are compared, and the ramp-suppression characteristics of the OWEJS are investigated. Second, chance-constrained programming is performed to construct a ramp-control model that considers the “source-storage-load” operating characteristics and offshore wind-power uncertainty. Finally, the CRITIC-TOPSIS comprehensive evaluation model is used to analyze the additional operating costs and uncertain resource-usage rates at different confidence levels to obtain the optimal confidence level. Simulation results show that under the same grid-power ramp-control conditions, the comprehensive operating cost of the offshore wind and hydrogen co-generation system is 0.29 million yuan, which is significantly lower than the 1.33 million yuan for offshore wind farms. When considering wind-power uncertainty, a confidence level of 0.98 can offer balance between cost control and risk mitigation.