The invention discloses a syringe for an injector. One end is provided with two slide cavities, and a separation plate is arranged between the two slide cavities; the other end is provided with a needle holder, the needle holder is provided with two liquid outlet holes, and each liquid outlet hole is communicated with a corresponding slide cavity; and the separation plate is a flat plate, and theslide cavity is in a semicircular shape or an arch shape. The syringe for the injector has the advantages that the syringe is matched with a needle and a piston, so that at least two medicine liquid can be injected only by requiring one-time acupuncture, and the pain of a patient can be effectively alleviated.