During the AC side fault crossing process of the Baihetan to Jiangsu ± 800 kV hybrid DC transmission project, controllable lightning arresters need to be installed to limit the absorption of redundant energy by overvoltage on the flexible busbar. In order to achieve 1 ms rapid input of controllable lightning arresters, it is necessary to develop a high-voltage DC trigger switch. According to the engineering requirements, a topology structure of trigger switch using trigger gap parallel fast mechanical switch was designed, and a fast trigger strategy is developed to clarify the design scheme and key technical parameters of trigger gap and fast mechanical switch. After verification of the trigger switch debugging waveform in the application of the Baijiang Project, the response speed and key technical indicators of the trigger switch fully meet the requirements of the Baijiang Project.