1. A safe syringe comprising: a cylinder that extends in an axial direction and includes a first tubular portion, a second tubular portion extending from the end of the first tubular portion, and a first folded ring resiliently mounted and formed on the inner side of the first tubular portion and located around the axis； after unfolding the first folded ring, the first folded ring is clamped and extends from the first tubular portion toward the second tubular portion and includes a first movable flexible portion； a piston including a rod located along the axis and inserted to move into the cylinder, and a plug, mounted on the end of the stem； a needle needle mounted detachably in a second tubular portion, a piston plug may be pressed in the needle head to stretch the first flexible portion so that the first flexible portion can separate from the needle head. 2. The safety syringe according to claim 1, wherein the piston can be moved to the injection position, the restriction position, and the removal position relative to the needle head； when the piston moves to the injection position, the piston plug is located in the first tubular portion and at a distance from the needle head, and the first flexible portion pushes the needle head, which must be secured in the second tubular portion； when the piston moves to the limit position, the piston is pressed in the needle head to stretch the first flexible portion, so that the first flexible portion is separated from the needle head； when the piston moves to the retraction position, the piston is positioned on1. Безопасный шприц, содержащий:цилиндр, который продолжается в направлении оси и включает в себя первый трубчатый участок, второй трубчатый участок, продолжающийся от конца первого трубчатого участка, и первое сложенное кольцо, упруго установленное и образованное на внутренней стороне первого трубчатого участка и расположенное вокруг оси； после раскладывания первого сложенного кольца первое сложенное кольцо зажимаетс
