Abstract: The present invention relates to a safety syringe. The safety syringe comprises a barrel having a plurality of elastic support units in the inner side, a plunger having a rubber ring and a first coupling portion at the front-end, and an injection head unit comprising a first needle seat, a second needle seat, and a needle, wherein the second needle seat comprises a second coupling portion. When the injection head unit is mounted on the front-end opening, the second needle seat is propped by the plurality of elastic support units preventing the needle seat from being crushed during injection. After injecting, the first coupling portion is pushed to couple with the second coupling portion, and then the needle can be pulled into the barrel for safety.