Abstract: A suit of optical diagnostics, including a fiber array detector, a solar-blinded fiber detector and a framing camera, was used to investigate the discharging process on multi-gap gas switch. Experiments were carried out to study the relationship between the delay time and various switch parameters. The ratio of the statistical delay to all delay time was 42% while the formative delay was 58%, and the delay time of third gap and fourth gap were principal part of trigger delay. The evolution of channel arcs were acquired with a framing camera. The characteristic of discharge channel image and the change of discharge channel numbers with different trigger voltage and gas pressure were analyzed. The trigger voltage had a considerable influence on the channel numbers of trigger gap, while no obvious influence on other gaps. More channel numbers with higher trigger voltage were observed. There were not combination and extinguishment of channel arcs and new channel arcs might emerge.