A firing actuator mechanism used in a toy gun is disclosed to include a trigger mechanism, a link having a push portion and a stop portion at the rear side thereof, a retaining mechanism formed of a holder block and a sliding block, a hammer and a locking block. The sliding block has an engagement portion at the front side, and a first side rod and a second side rod at one lateral side. When the link is moved backwards during a single fire mode, the push portion forces the first side rod to move the sliding block backwards. When the link is moved backwards and the rear end portion is forced downwards during a continuous fire mode, the stop portion is stopped against the second side rod of the sliding block. The hammer has a durable press portion lockable by the locking mechanism.