The invention is an assembly structure that allows molecular sieves and can-filters be fast assembled in an oxygen concentrator. The structure includes: a molecular sieve and can-filter set, which is composed of at least two molecular sieves and at least one can-filter; a support frame, which includes a base plate and a frame fixed on the base plate in an upright position, and the frame has a first support plate having a plurality of through holes and a second support plate having a hole, wherein the hole of the second support plate is for one of the at least one can-filter to pass through; and a plurality of bend joints, each of which including: a thin plate portion formed at a first end, wherein an opening is provided in the center of the thin plate portion; and a plurality of annular barbed portions provided near a second end, such that a flexible conduit/hose connected thereto does not detach easily and the air tightness is increased, wherein the second end of each bend joint passes through one of the through holes of the first support plate while the thin plate portion of each bend joint is fixed to the first support plate via a second fastener.