A trigger assembly for switching one shoot mode or repeat shoot mode includes a trigger, a switch, a fixing element, a trigger plate and a torsion spring. When a user wants to switch the shoot modes of the nail gun, the user turns the switch so that the fixing element moves along the curved track of the switch and the fixing element drives the trigger plate to move on a protrusion or on a through hole simultaneously. After the user presses the trigger, the trigger plate is resisted by the protrusion so that the nail gun is in one shoot mode. In addition, when the trigger plate is vibrating on the through hole, the nail gun is in repeat shoot mode.