A nail gun having a safe firing mechanism is composed of a main body, a nail-driving member, a safety member, and a linkage. The main body includes a nail passage for receiving nails and a nail chamber for receiving a nail ready to be fired by the nail-driving member. The nails include an initial nail, a final nail, and a plurality of standby nails located between the initial and final nails. The linkage includes a contact portion and a stopping end linking up with the contact portion. The contact portion is stopped against the standby nail. The stopping end is stopped against the safety member. When the contact portion is not stopped against the standby nail, the stopping end is located at where the safety member is stopped. When the contact portion is stopped against the standby nail, the stopping end shifts to where the safety member is not stopped.