The integration of offshore wind farms into the power grid often accelerates reactive power and voltage fluctuations in the access point area, rendering existing automatic voltage control (AVC) strategy insufficient to meet the reactive power regulation requirements. To address this, an energy-saving-oriented and practical method for setting reactive power optimization control intervals at grid connection points of offshore wind farms is proposed. First, considering the operational characteristics of offshore wind farms, the quadratic curve of active power loss in the grid connection area is investigated. Then, active output scenarios are categorized according to the active power output capacity of the offshore wind farm. By using the principle of minimizing active power loss differences to define the optimization cost, the reactive power optimization control interval is determined accordingly. Finally, a series of intervals under different scenarios are adjusted using the semi-invariant method to obtain the differentiated upper and lower limit values for reactive power control. Simulation experiments based on actual offshore wind farm grid connection scenarios show that the proposed method significantly improves energy efficiency and voltage stability in the grid connection area, offering an effective solution for reactive power control in offshore wind power integration.