Pig farm vaccine injection syringe with needle head capable of being automatically withdrawn and replaced

The invention relates to the technical field of vaccine injection, and discloses a pig farm vaccine injection syringe with a needle capable of being automatically withdrawn and replaced, the pig farm vaccine injection syringe comprises a syringe tube, a fixed outer ring is mounted outside the syringe tube, and a needle storage rim is mounted outside the fixed outer ring; four needle containing cavities evenly distributed in the annular shape are formed in the needle containing wheel rim, a magnet block is installed on one side of the outer portion of the fixing inner ring, an injector head is arranged on one side of the front end of the outer portion of the injector tube, and a needle fixator is installed outside the injector head. A needle head is installed at one end of the outer portion of the needle head fixator, and an inner cavity is formed in the needle head fixator. The limiting ball is limited through the metal block, so that the needle fixator is fixed through the limiting ball, and the needle fixat