A safety syringe, comprising a needle sleeve, with a first groove provided on an inner wall thereof; a needle base, with at least two first claws provided on an outer wall thereof, the first claws being configured to clamp in the first groove; a core rod, sealedly and slidably arranged in the needle sleeve; wherein one of a proximal end of the needle base and a distal end of the core rod is provided with at least two second claws, and the other one is provided with a position-limiting member; the second claws are configured to abut against the position-limiting member along a slanted surface; in an injecting state, when the core rod slides towards a distal side, the second claws are forced to slide along the slanted surface and deform in a radial direction of the needle sleeve under the action of the slanted surface, so as to pass over the position-limiting member and become hooked onto the position-limiting member; in the injecting state or a retracting state, the core rod slides to drive the first claws to slip out of the first groove, a mounting cavity of the needle sleeve comprises a needle base chamber and a transition chamber communicated with the needle base chamber; characterized in that, the mounting cavity further comprises a position-limiting chamber communicated with a proximal end of the transition chamber; the position-limiting chamber has an inner diameter larger than that of the transition chamber, and a second stepped structure is formed between the transition chamber and the position-limiting chamber; the safety syringe further comprises an elastic position-limiting ring fixed on an outer wall of the core rod; a position-limiting protrusion is provided on an inner wall of the position-limiting chamber; an outer diameter of the elastic position-limiting ring in a free state is at least larger than an inner diameter of a proximal end of the transition chamber, and is also larger than an inner diameter of the position-limiting protrusion; in the retracting state, a distal end of the elastic position-limiting ring is constrained in the position-limiting chamber by a proximal end face of the second stepped structure, and a proximal end of the elastic position-limiting ring abuts against the position-limiting protrusion. a needle sleeve, with a first groove provided on an inner wall thereof; a needle base, with at least two first claws provided on an outer wall thereof, the first claws being configured to clamp in the first groove; a core rod, sealedly and slidably arranged in the needle sleeve; wherein one of a proximal end of the needle base and a distal end of the core rod is provided with at least two second claws, and the other one is provided with a position-limiting member; the second claws are configured to abut against the position-limiting member along a slanted surface; in an injecting state, when the core rod slides towards a distal side, the second claws are forced to slide along the slanted surface and deform in a radial direction of the needle sleeve under the action of the slanted surface, so as to pass over the position-limiting member and become hooked onto the position-limiting member; in the injecting state or a retracting state, the core rod slides to drive the first claws to slip out of the first groove, a mounting cavity of the needle sleeve comprises a needle base chamber and a transition chamber communicated with the needle base chamber; characterized in that, the mounting cavity further comprises a position-limiting chamber communicated with a proximal end of the transition chamber; the position-limiting chamber has an inner diameter larger than that of the transition chamber, and a second stepped structure is formed between the transition chamber and the position-limiting chamber; the safety syringe further comprises an elastic position-limiting ring fixed on an outer wall of the core rod; a position-limiting protrusion is provided on an inner wall of the position-limiting chamber; an outer diameter of the elastic position-limiting ring in a free state is at least larger than an inner diameter of a proximal end of the transition chamber, and is also larger than an inner diameter of the position-limiting protrusion; in the retracting state, a distal end of the elastic position-limiting ring is constrained in the position-limiting chamber by a proximal end face of the second stepped structure, and a proximal end of the elastic position-limiting ring abuts against the position-limiting protrusion.