A combustion powered nail gun includes a combustion sleeve moveable between a sealed position and an open position; a trigger switch having a first hook portion; a safety lever pivotally mounted in a housing and provided with a second hook biasable to be engaged with the first hook portion; and a restriction member connected to and moveable along with the combustion sleeve in a way that when the combustion sleeve is in the open position, the restriction member is stopped at the safety lever in which the second hook portion is engaged with the first hook portion so as to lock the trigger switch, and when the combustion sleeve is in the sealed position, the restriction member is spaced away from the safety lever to enable the second hook portion to be biasable away from the first hook portion so as to unlock the trigger switch.