A syringe (1) is used by combining a pharmaceutical agent bottle (2) and a needle (3). The syringe (1) comprises an outer protective housing (10) an engagement sleeve ring (20) a pharmaceutical agent bottle sleeve housing (30) an inner canula (40) a two way helical guide pipe group (50) a screw connection ring (60) a one way ratchet (70) a helical plunger (80) and an injection plunger group (90). The engagement sleeve ring (20) is arranged at a front end of the outer protective housing (10) and is combined with the pharmaceutical agent bottle sleeve housing (30) to arrange the pharmaceutical agent bottle (2) in a group manner. The inner canula (40) the two way helical guide pipe group (50) the screw connection ring (60) the one way ratchet (70) the helical plunger (80) and the injection plunger group (90) are arranged in a group manner inside the outer protective housing (10). A user can quickly pull the injection plunger group (90) backwards in a straight direction and then push the injection plunger group (90) in the straight direction to perform injection. With the help of large pitch stroke construction of the two way helical guide pipe group (50) in conjunction with a screw hole (61) of the screw connection ring (60) and small pitch stroke construction of the helical plunger (80) straight pressing force is converted into rotation force and large stroke rotating push force is converted into small stroke rotating injection push force thereby achieving a purpose of quantitative pharmaceutical agent injection and achieving an effort saving effect by means of a simple operation manner of circulating opening and closing.
