A braking mechanism for empty nail cartridge of a nail gun includes a guiding plate, a cover plate, a punch rod, a securing slide rod and a nail cartridge. A nail hole and an end hole are defined in the guiding plate having a connecting groove. A nail pusher and a pushing arm are arranged in the nail cartridge to provide resilient force along a nail firing direction. The pushing arm is pivotably placed on the nail pusher adjacent the brake portion for affording the resilient force. The pushing arm allows the brake portion of the nail pusher to go through the end hole and move into the end hole to block the stopper of the securing sliding rod when the nails are used up. The pushing arm moves into the connecting groove to improve the yield rate of the brake of the empty nail cartridge of the nail gun.