A syringe (1) cycling switch mechanism, comprising an inner barrel (40), a bidirectional helical guiding barrel assembly (50) disposed inside of the inner barrel (40), and an injection plunger assembly (90) disposed inside of the bidirectional helical guiding barrel assembly (50). The bidirectional helical guiding barrel assembly (50) comprises an outer helical guiding barrel (51) and an inner helical guiding barrel (52) disposed inside of the outer helical guiding barrel (51). The rear end of the inner helical guiding barrel (52) is connected via a pin joint with the plunger end cover (92) of the injection plunger assembly (90). The outer helical guiding barrel (51) and the inner helical guiding barrel (52) cooperate via a helical guiding groove (514) and a helical guiding block (521), such that the inner helical guiding barrel (52) can rotate and move forward within the outer helical guiding barrel (51). The outer surface of the inner helical guiding barrel (52) is provided with multiple non-return ring threads (522) and an axial guiding groove (523). The inner barrel (40) uses a non-return protrusion (42) thereof to switch position between the non-return ring threads (522) of the inner helical guiding barrel (52) and the axial guiding groove (523). During each operation, the injection plunger assembly (90) can be rapidly pulled back axially. When the injection plunger assembly (90) is pressed axially again, the axial push force is converted into a rotational push force via the bidirectional helical guiding barrel assembly (50) to inject a set dosage of medicine. The cycling switch operation mode achieves simple operation and force conserving.Linvention concerne un mécanisme de commutation circulaire pour seringue (1), comprenant un cylindre intérieur (40), un ensemble cylindre de guidage hélicoïdal bidirectionnel (50) disposé à lintérieur du cylindre intérieur (40) et un ensemble piston dinjection (90) disposé à lintérieur de lensemble cylindre de guidage hélicoï
