A safety syringe includes a barrel, a plunger, and a needle hub. The barrel is extended axially and includes a first tube portion, a second tube portion extended from an end of the first tube portion, and a first folded ring flexibly branched and formed on an inner side of the first tube portion and disposed around the axis, such that after the first folded ring is unfolded, the first folded ring is bounded and extended from the first tube portion towards the second tube portion, and includes a movable first flexible portion. The plunger includes a rod extended along the axis. The needle hub is detachably installed in second tube portion. The plunger can be moved to an injecting position, a limit position, and a disposal position with respect to the needle hub.
