A nail gun includes an air chamber, a main air passage, and a trigger valve with a valve body is disposed between the air chamber and the main air passage. The trigger valve includes a valve bar, an air exhausting passage an air guiding passage and a stopper. The stopper divides the valve body into an upper air chamber and a bottom air chamber. The upper air chamber is connected with the air chamber via the air guiding passage. The bottom air chamber is connected with the upper air chamber via at least one connecting passage disposed in the upper bar portion.