Abstract: According to the technical requirements put forward by Baihetan-Jiangsu ±800 kV UHV DC transmission project, a parallel controllable gap for controllable arrester is designed and studied in view of the fact that the controllable gap action time gap cannot maintain the conduction state to the mechanical switch action when the system overvoltage amplitude is low. Through the supplementary Mayr arc model, the relationship between the energy injected by the trigger and the gap arc maintenance time under given conditions is analyzed and predicted, and an experimental platform is set up to study the influence of the power and energy provided by the trigger on the gap arc maintenance time. The results show that increasing the power and energy of the trigger can increase the time of the maintain combustion of gap arc. When the energy of the main circuit of the gap is insufficient, the energy provided by the trigger can be used as the standard to measure the minimum conduction capacity of the gap. Finally, the gap can be kept on for 5 ms when there is no energy injection in the main circuit through the way of successive triggering with an interval of 1 ms by five triggers, which has the ability of seamless timing coordination with the fast mechanical switch. The results can provide theoretical supports for the promotion of the scheme of controllable arrester with parallel controllable gap.