Abstract: A power staple gun including a gun body having a staple nozzle at one end and a coupling frame at an opposite end, a magazine connected between the staple nozzle and the coupling frame to hold staples, and a follower member for pushing the staples toward the staple nozzle, wherein the magazine defines different pairs of staple grooves for loading staples of different lengths, having a staple loading port at one side for loading staples into one pair of staple grooves, the staple loading port having a straight top side, a straight bottom side being an elongated through hole, a straight lateral side and a stepped lateral side bilaterally connected between the straight top side and the straight bottom side, the stepped lateral side having steps corresponding to the pairs of staple grooves and being marked with marks for indexing the loading of different sizes of staples.