reference to fig3 for a moving braking unit 200 of the present invention the moving braking unit 200 is comprised of a snap in frame 2 and a chain 4 flexibly connected to the snap in frame 2 wherein the snap in frame 2 can enter or exit the cartridge 3 a safety curtain structure of the present invention comprises a hub 1 a hanging portion 11 formed on an external surface of the hub 1 and provided for combining a rod not shown in the figure of a curtain a driven wheel 10 pivotally installed in the hub 1 a universal driving shaft 12 extended outwardly along the axis of a axial center of the driven wheel 10 and used for rolling the curtain a cartridge 3 coupled to a lower circular tangent position of the hub 1 and comprising a cartridge opening 30 a joint plate 301 and a joint plate 302 wherein planes of the joint plates 301 and 302 are perpendicular to the axial center of the universal driving shaft 12 a pivot hole 31 separately formed on the joint plates 301 302 penetrated through the front and the back and disposed at a linear position parallel to the axis of the axial center and a first kidney shaped hole 32 and a second kidney shaped hole 33 being.