This paper summarizes the structural design and experimental study of UV pre-ionizing for multi-gap gas switch. The structures of needle UV pre-ionizing and hole UV pre-ionizing are designed. Static properties of switches with three trigger structures are obtained. There is no evident change of static field in switches and the change of self-breakdown voltage is under 3% with UV pre-ionizing. The jitter of UV pre-ionizing switches is about 20% less than that of the switch without UV pre-ionizing. The needle UV pre-ionizing method can lower the trigger voltage by 10 kV, and the hole UV one by 5 kV. For needle UV pre-ionizing, the UV intensity with different trigger voltages, gas pressures and distance of UV gap are measured. The optimum distance of UV gap is experimentally determined as 1.5