The ±500 kV valve halls of wind farm offshore platforms are integrated through a high-voltage direct current (HVDC) transmission system and constructed in deep-sea conditions, making the design of net air clearance distances particularly critical. This paper investigates key factors influencing air clearance distances associated with the impulse overvoltage characteristics of the main equipment in the valve hall. Based on the preliminary design of a ±500 kV offshore converter valve hall, critical air gaps were determined. The full-scale samples were employed to conduct standard switching impulse overvoltage tests. In this way, the overvoltage discharge characteristics of air gaps in the offshore converter valve hall were obtained. Finally, based on the air gap configuration method and the obtained discharge characteristic data, a recommended net air clearance distance range is proposed for the ±500 kV valve hall of the offshore platform, providing a vital reference for the compact design of offshore wind farm valve halls.