DISPOSABLE SYRINGE

A disposable syringe, comprising a pen holder sleeve (11), wherein a rear cover (12) is clamped and mounted to a rear end of the pen holder sleeve (11); a pen cap (13) is provided at a front end of the pen holder sleeve (11); a trigger pressing assembly (2) is provided inside the front end of the pen holder sleeve (11); and an air source pushing injection assembly (3) is provided inside a middle portion of the pen holder sleeve (11). By means of making a front end of a pre-filled needle (321) be in contact with a patient's muscle surface and then directly pressing, when the pre-filled needle (321) pierces the skin's surface, a trigger sleeve (21) presses backward under the limiting action of a limiting sleeve (22), so as to push a pressure drive rod (35) to directly pierce a sealing film at a front end of a compressed air source (36), such that compressed air inside the compressed air source (36) is instantaneously released to push a pre-filled rubber plug (34) inside the pre-filled needle (321), and then a l