The invention discloses a small-gap gas switch for a high-voltage pulse generator. The small-gap gas switch comprises a switch positive electrode and a switch negative electrode, wherein the switch positive electrode and the switch negative electrode protrude towards opposite sides in ellipse shapes, a switch trigger electrode is arranged between the switch positive electrode and the switch negative electrode, two ends of the switch trigger electrode are in ellipse shapes and are sunken towards centers, gaps are formed among the two ends of the switch trigger electrode, the switch positive electrode and the switch negative electrode, the gaps change with sunken curves of two ends of the switch trigger electrode and are gradually reduced towards a direction near to the center of the switchtrigger electrode. The gas switch which is fast in switch conduction and having relatively low delay jittering is achieved.