The invention discloses a rodless cylinder. The rodless cylinder comprises a cylinder body, a piston body, an outer steel strip, an inner steel strip, two piston heads and two end covers; a sliding groove is formed in the cylinder body; a piston end of the piston body is arranged in the cylinder body; a sliding block end of the piston body penetrates through the sliding groove and is arranged outof the cylinder body; the outer steel strip and the inner steel strip are respectively mounted between the piston body and the exterior of the cylinder body and between the piston body and the interior of the cylinder body; the two end covers are respectively mounted at the two ends of the cylinder body; the two piston heads are respectively arranged at the two ends of the piston end of the pistonbody and extend into the piston end; pin holes are formed in the surfaces of the piston heads; mounting holes are formed in the surface of the piston ends corresponding to the pin holes; the piston heads are connected with the piston ends through locking pins; the locking pins, the mounting holes and the pin holes are matched for locking. According to the rodless cylinder, the production cost isgreatly reduced on the premise of ensuring connecting stability.