750 kV AC to DC technology has been widely applied in the interconnection project of Xinjiang and the northwest main network. To ensure the safe operation of the transmission line after the conversion, the insulation configuration of the transmission line must be reconfigured, which generates numerous tower head air gap calculation requirements. However, the existing gap circle verification method relies solely on manual drawing for calculation, resulting in low calculation efficiency. Therefore, this paper extracts the key calculation parameters of the tower head air gap and proposes a fast calculation method of the tower head air gap suitable for 750 kV AC to DC transmission lines. The method has been applied in the two-channel interconnection transmission project of the 750 kV Xinjiang and Northwest main network. The results show that the proposed method can control the calculation error within 3% by reducing the difficulty of data collection, which provides technical support for the rapid calculation of large-scale tower head air gaps.