A nail gun nozzle mechanism includes a clamping wall, a retaining wall, and a switch unit. The clamping wall defines a firing space. The retaining wall defines a withdrawn space that is in spatial communication with the firing space. The switch unit includes a linkage member, and a bracket member. The bracket member is movable relative to the clamping wall between a firing position, where the bracket member is distal from the clamping wall and is disposed in the withdrawn space, and a non-firing position, where the bracket member is proximate to the clamping wall and blocking at least a portion of the firing space. The linkage member resiliently biases the bracket member toward the non-firing position.