Abstract: Factors affecting the triggering breakdown characteristics of a multi-gap gas switch have been investigated in this paper. Experiments were carried out to study the relationship between the trigger jitter and various switch parameters, e.g. the trigger voltage, the switch pressure and the ultraviolet (UV) pre-ionizing duration. Results indicate that the trigger jitter decreases evidently with the trigger voltage changing from 50 kV to 80 kV, and the statistical delay jitter decreases more evidently than the formative delay jitter. Both the statistical delay jitter and the formative delay jitter increase with the gas pressure changing from 0.16 MPa to 0.28 MPa. The trigger jitter and the formative delay jitter also decrease when the duration of the UV pre-ionizing is prolonged. The optimized duration of UV pre-ionizing is 80-140 ns and the trigger jitter decreases by about 39%. The UV pre-ionizion could effectively reduce the statistical delay jitter, but has little effect on the formation of delay.