In recent years, the rapid development of offshore wind power has been affected by the construction period of the power grid. Sometimes it is necessary to arrange a grid-connected transitional operation plan to increase the utilization rate of offshore wind power. Taking offshore wind power in a certain area of Guangdong as an example, this paper evaluates the oscillation risk of planning schemes and transitional operation schemes, and studies the calculation method of short-circuit ratio under the mode of convergent and grid-connected multiple wind farms and the principle of determining the grid-connected capacity of wind power and the influence of centralized control station static var generator (SVG) on grid-connected capacity. Results show that offshore wind power is connected to the grid via AC submarine cables, and there is a strong interaction between wind turbines and SVGs and the AC grid, which makes the wind power grid-connected system at low wind speeds have a risk of oscillation. Moreover, the capacity of the SVG used to compensate the reactive power of submarine cable charging at the centralized control station limits the grid-connected capacity of wind power. Therefore, the SVG capacity needs to be considered when calculating the wind power grid-connected capacity according to the short-circuit ratio. On this basis, technical measures of increasing the grid-connected capacity of offshore wind power are proposed to meet the operational requirements of the grid-connected transition plan.