Abstract: A safety syringe comprises a needle set, a barrel and a plunger. Wherein the front end of the needle set is connected with a needle, while the rear end is provided with a first coupling portion; the bottom of the needle set has on the periphery thereof at least an annular flange. The barrel is hollow, its front end is formed as a socket to connect the needle set; the socket has on its inner wall two mutually neighboring annular flanges. The rear end of the barrel is used for slipping in the plunger of which the front end has a piston; a second coupling portion is provided on the front end of the piston. Hence when the needle set is connected to the needle-set socket, the said at least an annular flange on the periphery of the needle set is located between the two annular flanges on the inner wall of the needle-set socket to increase the tightness of connection.

Abstract: A retractable type safety syringe comprises a needle set, a barrel and a plunger, wherein the needle set has a first engaging portion on the bottom thereof. The front end of the plunger has a contractible elastic piston. The piston has a second engaging portion on the top thereof to be engaged with the first engaging portion. When the piston is pushed into the injecting space of the barrel to contact the inner wall on the top end of the injecting space, and when a force is exerted to make the first engaging portion connect with the second engaging portion, the piston can restore from the deformed state to overcome the fixed connecting force of the needle set. The safety syringe has a variety of feasible shapes and structures of pistons that can suit various retractable type safety syringes.

Abstract: The retractable safety syringe for drawing back a soft piston therein is comprised of a needle set, a cylindrical barrel and a plunger. A retractable mechanism is provided for pulling the needle set into it. The plunger is provided on the front end thereof with a soft piston, and with an activating piece to activate the retractable mechanism or with a connecting piece connectable to the retractable mechanism. When in assembling, the soft piston of a plunger is pushed to the top point of a space provided for injection, before deformation of the piston, an activating piece or a connecting piece on the plunger does not activate or connect with the retractable mechanism, and when the plunger is pushed by a force larger than a preset amount, the piston is compressed to deform and to render the activating piece to activate or connect with the retractable mechanism to pull the needle set into the cylindrical barrel automatically or manually.