The present application discloses a lockable fitting structure used for an electric air-purifying
respirator of an auto-darkening
welding helmet, the electric air-purifying
respirator comprising a housing and a battery device, a
battery holder being formed in the housing, and the battery device being able to be detachably installed in the
battery holder by the lockable fitting structure, wherein the lockable fitting structure comprises at lease four pairs of sliding joint structures formed on the battery device and the
battery holder respectively and a locking structure provided in the battery device, wherein the sliding joint structures of each pair can be engaged with or disengaged from each other by sliding them relative to each other, wherein the locking structure comprises a button and a tongue capable to be actuated by the button, wherein the tongue is movable along a direction substantially perpendicular to a sliding direction of the sliding joint structure, and wherein after the sliding joint structures have been moved relative to each other in place, the tongue contacts a stop side of the battery holder to lock the pairs of sliding joint structures. The present application also discloses an electric air-purifying
respirator for an auto-darkening
welding helmet, which is equipped with said lockable fitting structure.