Abstract: The primary objective of China Fusion Engineering Demonstration Reactor (CFEDR) is to bridge the technical and industrial transition from the International Thermonuclear Experimental Reactor (ITER) to prototype fusion power plants, demonstrating the feasibility of sustained high-power, safe, and stable fusion energy operation. As one of CFEDR's crucial auxiliary heating methods, the Ion Cyclotron Resonance Heating (ICRH) system requires 20 MW power input for Conventional-H mode operation. The antenna system will feed 20 MW of power through a mid-port plug-in, which constitutes a vital component of the antenna system. To meet the demands of high-power, long-pulse operation, the Port Plug necessitates active cooling and high-vacuum sealing to ensure system reliability and safety. This study proposes a novel cooling structure design that balances structural integrity with manufacturing feasibility, based on the functional requirements and cooling circuit constraints of the ICRH antenna Port Plug. Through fluid-thermal coupled numerical simulations using ANSYS Fluent, we systematically analyzed the flow characteristics and cooling performance of the Port Plug's cooling circuit. Key findings include: (1) Velocity distribution demonstrates synergistic “acceleration in contraction zone (peak 16.7 m/s) - moderated flow in milled channels (90% area <1.5 m/s)”, achieving optimal balance between high-heat zone cooling and low flow resistance; (2) Pressure gradient analysis validates channel design rationality, with inlet pressure of 9.06 MPa and total pressure drop of 5.06 MPa, meeting the <6 MPa design constraint; (3) Temperature field analysis shows fluid outlet temperature of 105℃ (ΔT=35℃) below 50℃ threshold, and panel temperature difference of 564℃ within 650℃ limit. The simulation results confirm that the cooling circuit satisfies both thermal and hydraulic design requirements. This research provides essential theoretical foundations for the engineering design of the ICRH antenna Port Plug in CFEDR.