The utility model discloses a self sealss formula pneumatic cylinder piston locking device belongs to pneumatic cylinder technical field. Including piston rod and piston, piston rod one end is opened threadedly, and the piston passes through threaded connection and installs at the piston rod thread end, piston end opens has the one or more recess placed a piece in the recess, the upper end cooperation of book piece is rolled over an other end and is connected through welding and piston rod thread end surface in inserting piston end's recess. The utility model discloses do not have the clearance between well piston and the piston rod, with the cooperation of the boss on the shang rod half the circumference of the sleeve where it joins the shoulder with the heavy groove of piston internal surface, the leakproofness obtains great improvement again, using and rolling over fixed piston of piece and piston rod, the piston rod thread end does not have other processing, and manufacturing procedure is few, and production efficiency is high, and is locking more reliable.